We all want to live in small towns, and it’s killing cities

Downtown Northfield, MN

A bunch of economists and a blogger are trying to dissect the riddle of why metropolitan population density has fallen in the United States. Robert Shiller (yes, that Robert Shiller) seems to have unknowingly kicked off the whole thing when he wrote an essay a few weeks ago in which he said housing prices have actually been pretty stable when you adjust for inflation.

Bill McBride took issue with that, essentially saying that because land is scarce in cities, the value of the land (and the homes on it) should go up. Noah Smith didn’t quite agree with McBride, arguing that changes in transportation cost—everything from automobiles to telepresence—will counter the effects of population density over time, which is why house prices should remain flat. Paul Krugman jumped in and sided with Smith, mostly, citing the issue of declining metro population density across the United States.

Then Felix Salmon, the blogger, entered the picture. He wrote a post a few days ago laying out his solution to the riddle of why metro population density is declining. Rich people, he says, are moving to the city in larger numbers, and because they can afford more space, urban population densities are either holding steady or falling. That’s been pushing less wealthy people out to the suburbs and beyond. I’m skeptical that’s the real reason.

Most of the previous decade’s growth in the U.S. happened in the exurbs, those far flung outposts on the fringes of metro areas. There, populations rose by about 5 percent, much higher than the zero to 2 percent elsewhere throughout metro areas, including low-density but closer-in suburbs. People forgoing suburbs for the exurbs—that’s a nuance of the statistic that makes me question Salmon. If people are being driven out of the city because of high rents, then the suburbs should be growing swiftly, too. But they’re not—at least not as much as the exurbs.

Rather than reacting to what the rich are doing in the city, I think it’s more the result of how most of the rest of us would like to live. The exurbs are closer, by many measures, to the small town American ideal than the city or even the suburbs. Exurbs have single-family homes, big lots, wide streets, and a nearby countryside. The city doesn’t have that, and many suburbs don’t anymore, either—as cities swell, they’re becoming indistinguishable from the city. The exurbs are the new suburbs.

Krugman tries to drive home his point, saying, “the average American lives in a quite densely populated neighborhood, with more than 5000 people per square mile.” As such, he says, “real” America isn’t a small town, but rather something like metropolitan Baltimore. By pure statistics, he’s right. But that doesn’t necessarily mean the U.S. is a country trending toward Baltimore. A statistical snapshot can’t outweigh decades of cultural legacy. Most Americans may live like Baltimoreans, but do they want to?

Our cultural tendencies suggest we don’t. As long as the American ideal is to live in a small town—which to many people¹ means big yards, small downtowns, and concomitant low population densities—then that’s where we’re heading as a nation. If cities are to succeed, maybe they need to look to small towns for inspiration. Not the low densities—it wouldn’t be much of a city, then—but the more abstract qualities that draw people to them.

Not necessarily me, though that’s a post for another time. ↩

Photo by Northfielder.

How population density affected the 2012 presidential election

How far should you live from work?

Can you tell urban from rural?

If you were given a section of a map, could you tell if was from a city or the countryside? The answer to that question may be trickier than you expect. I pondered this a year and a half ago when I wrote, “ ‘countryside’ is inherently interpretable term, one that depends more on how the land is used than it does on population density.”

It first struck me when I was traveling around Taiwan. There, the distinction between the rural and urban areas wasn’t always apparent to my Western eyes. The same can be true with maps. Distinguishing between urban and rural depends as much on geographic and cultural contexts as it does on visual cues like road networks.

Can you tell which is which?

The following maps are road networks from a variety of locations around the globe. Guess which are cities and which are rural areas. All maps are drawn to the same scale.

From top to bottom: 1. city (Denver) 2. countryside (Japan) 3. city (New York City) 4. city (Houston) 5. countryside (Taiwan) 6. city (Los Angeles) 7. countryside (Wisconsin)

Related posts:

What do we mean by “rural”?

Income inequality, as seen from space

If the world’s population lived like…

What are the odds a meteor will destroy a city?

Risk of an asteroid destroying a city

Sources:

Ivezic, Zeljko. 2013. Personal communication.

Schneider A., Friedl M.A. & Potere D. (2009). A new map of global urban extent from MODIS satellite data, Environmental Research Letters, 4 (4) 044003. DOI: 10.1088/1748-9326/4/4/044003

How population density affected the 2012 presidential election

There are lots of reasons why the 2012 presidential election broke the way it did, but one that’s not often reported—but particularly germane to Per Square Mile—is the divide between cities and the country. I’ve been thinking for a while now about this split as a driving force behind the polarization of U.S. politics, and I know I’m not alone. (On election night, Adam Rogers tweeted as much.)

But I was curious. Can we actually see the divide between cities and the country in the electoral map? In short, yes, but I’ll let the maps to the rest of the talking.

Swipe back and forth to see how population density relates to each candidates’ electoral result.

Thanks to Andy Woodruff of the always interesting Bostonography for the shapefile of the election results.

Related posts:

Income inequality, as seen from space

Redrawing the United States of America

Ghosts of geography

When everyone lives in a city

The future?

Here’s a fun thought experiment. Plot the population of the world since 500 BCE. Now plot the population of the 50 largest cities over that same time. If you distill equations to describe the two trends, you’ll notice the lines cross. At some point in the future, your models predict that the population of the 50 largest cities will overtake the world’s population. Clearly that’s impossible.

What those trends are telling you is that cities are growing faster than rural areas, something we already know. But if you take that thought experiment to its mathematical extremes, you’ll see it’s possible that there comes a point when—boom—everyone lives in a city. Rural dwellers—poof—cease to exist. Suddenly, we’re all children of the concrete jungle.

That’s what Michael Batty, a well-known urban planner and geographer, noticed when he ran through those same hypotheticals. Specifically, he calculated that by 2092 all the world will be urbanized according to those trend lines. Of course that won’t happen, and he acknowledges that. The world’s population will, at minimum, be equal to the sum of its cities, and I’m 100 percent certain that at least a handful of people will still live in the country, either by choice or chance. But Batty’s idea bears consideration. What would the world look like when, as he puts it, “all the world’s a city”?

The United Nations currently estimates the world’s population will reach 10 billion by 2100, just a few years after mathematics suggests we could all be living in cities. Now, that’s not to say the Earth would be covered by one massive city. Cities may be expanding outward faster than their population growth would warrant, but 10 billion people spread across all continents but Antarctica would live at a density of about 190 people per square mile (74 per square kilometer). Hardly a city.

But what if our notion of a city changed? A single definition is already maddeningly difficult to nail down. Take New York City, for example. It has about 8.2 million people within the polity, but the greater region has over 22 million. Where does New York really end? Houston and Tokyo, on the other hand, encompass too much. Each political entity contains vast tracts of undeveloped land. It’s clear that political boundaries aren’t adequate. So instead, what if we think of a “city” as a collection of conurbations not connected by geography but by social and economic ties, as Batty suggests? In an age of plane travel and high-speed rail, physical continuity isn’t necessarily a requirement.

With this new definition, it is possible for all the world to be one city. The Earth doesn’t have to be covered in conurbation; rather, everyone simply has to live in urban areas, and those urban areas must be sufficiently connected so as to behave like a single city.

Already metros and their regional governments cross existing political boundaries. New York City is a perfect example. And at the other extreme, there are cases like Tokyo where city governments have essentially absorbed their hinterland equivalents. (We see this all the time in the United States with combined city and county governments—New York City, San Francisco, and Lexington, Kentucky, to name a few.) These mergers grew out of necessity, and it’s easy to see the same happening in a hyper-connected world. As more and more cities join the global cluster, as Batty calls it, the pressure to coordinate will rise.

It’s possible, then, that the first true world government could emerge from this collection of cities. It would be fitting. Already mayors from around the world meet to discuss common problems, and on issues like climate change where national governments have fallen flat, they have taken the lead. But it would still be a shift of epic proportions. It wouldn’t happen overnight, but at a certain point it would be inevitable. Cities could choose to sit on the sidelines, but the benefits of joining the global cluster would be too great to ignore. Eventually, nearly everyone on Earth would count themselves a resident of the One City.

The world as one city would surely be a different place. The relationship between a city and its hinterland would be tested. Indeed, what would become of the hinterland? It would certainly be smaller—although the One City wouldn’t smother the planet, it would still have an enormous footprint. The hinterland would remain inhabited by scattered few who choose to live there, perhaps living their quiet lives amongst robotized farms. A great schism between the city and the hinterland could develop. But there could also be a reconciliation. Governments could reconfigure to cope with the changing landscape, both literal and figurative. Instead tension between the city and its hinterland, there could be cooperation fostered by a sense of shared fate. So goes the city goes the hinterland, and vice versa.

Regardless of how it all plays out, a highly urbanized global population will add nearly 6 billion people to cities that only hold about 3.6 billion today. That’s growth of almost 280 percent in less than a century. Such a percentage isn’t unprecedented—between 1900 and today, the world’s urban population grew by more than 1600 percent—but the raw numbers will be. To accommodate those people, cities will have to remake themselves like never before. It’s a daunting challenge, and as I stated in my last article, we’ll need a science of the city that’s equally formidable.

Sources:

Batty, M. (2011). When all the world’s a city, Environment and Planning A, 43 (4) 772. DOI: 10.1068/a43403

United Nations. 2011. “World Urbanization Prospects, the 2011 Revision.” Accessed October 8, 2012.

Photo by kevin dooley.

Planet of the Cities

If the world’s population lived like…

How far should you live from work?

Rush hour, New York City

Thirty minutes at most, according to the wisdom of the crowds.

That comes from reams of data and piles of research that suggests commute times tend to cluster around this point. People tend to be good at weighing their options, economists think. If you live farther from work, you can usually afford a bigger house or apartment. But there’s a point where that journey becomes too onerous, and you are willing to sacrifice some of those desires to live closer to your job. That point on average seems to be between 20 and 30 minutes.

I was inspired to look into this further after seeing an article by Charlie Gardner over at his blog, The Old Urbanist. Gardner had mined the American Community Survey for average commute times in major metropolitan areas. Though there was a tight correlation between population and commute time (metros with larger populations have longer average commutes), the differences weren’t pronounced. They ranged from a low of 22.5 minutes in Kansas City to a high of 34.6 in New York City. That’s not a lot.

But before we ask why commute times hover in a tight band, perhaps we need to ask why people commute so far in the first place. Why not work next door? The answers may seem obvious, but what’s readily apparent to one person may not be to another. That’s why we examine these things scientifically. Well, in this case your hunch is probably correct. An older study by Martin Wachs and his colleagues at UCLA found, unsurprisingly, that people choose where to live not just based on commute times but also neighborhood characteristics, schools, and safety.

Now we can move on to the more curious question, why commutes tend to average 20-30 minutes. It’s not just limited to the United States, either. In the Netherlands, the average commute time in the early 2000s was about 28 minutes. Many European nations average about 35 minutes. What makes a half-hour so universal in terms of commuting?

It didn’t used to be that way. Average commute times in 1980 were around 22 minutes. Today, they’re around 25 minutes. Three minutes may not seem like much, but remember it’s an average. To increase an average by that amount, some commutes had to grow significantly to counter those that shrunk or remained the same. Now, keep in mind there is a lot of variation about those averages. Some people travel 2 minutes to work, others well over an hour. But on average, they have increased.

What’s causing that lengthening is higher job densities in major metros. Job growth is requisite to economic growth, and vice versa. As metro areas add more jobs, those jobs tend to be concentrated in business districts (after all, not everyone can work out of their homes). And as business districts fill up, commute times lengthen because the roads leading there become more congested. So when the economy booms, traffic slows to a crawl. I heard anecdotal evidence of this when I lived in San Francisco. People told me, if you think traffic is bad now, it was much worse during the tech boom of the late 1990s. When all those tech workers lost their jobs, gridlock practically evaporated, they said.

Subtle changes in urban form may also cause longer commutes. One study in the Netherlands and another in Quebec, found that polycentric metro areas—those with two or more cities, like Minneapolis-St. Paul—tend to have longer auto commute times. As cities grow and begin bumping into one another, such agglomerations are likely to become more common. It’s possible commute times may increase as well. While there may not be consensus on this point, I haven’t found any studies that claim changes in urban form will shorten commute times. That makes sense if you look at somewhere like New York City, which is both monocentric and dense. People may work a short distance from their homes, but traffic is so congested and public transit makes so many stops that commute times are still relatively long. Simply increasing density in some cities may shorten commutes for a brief period, but the honeymoon won’t last forever.

Which is a bummer, because for the most part people think their commutes are too long. A survey of 2,000 commuters in the San Francisco Bay Area reported that 52 percent of respondents said they commuted at least 5 minutes longer than they would like. Among that group, median commute times were 40 minutes, which is certainly longer than the region’s average. On the other hand, 42 percent said their commutes were just right (their median time was 15 minutes). Surprisingly, 7 percent felt their commute was too short (median of 10 minutes). But despite the fact that a majority think their commute is too long, most people said they didn’t mind it, so long as their trips were less than 100 miles.

That people don’t mind their commute may be why commute times refuse to shrink. People in the Bay Area survey who didn’t mind their commute said they agreed with statements like, “I use my commute time productively” and “My commute trip is a useful transition between home and work”, which supports anecdotal evidence I’ve heard that people enjoy the separation between work and home. Twenty to thirty minutes may be just enough time to unwind.

It’s not entirely universal, though. Tolerable commute times seem to lengthen when people switch from cars to mass transit. People may find that time more productive, or maybe the time seems shorter because driving can be stressful, while just sitting usually isn’t. Personally, I know I’m willing to commute longer by train than car. Another reason is because mass transit commutes tend to be more reliable in terms of duration (at least for trains). Not having to worry about traffic jams doubling your commute is a big advantage.

Regardless of mode, people seem to settle on an ideal commute time. And once they have settled, they don’t seem to stray from it. A study of two metro areas in Washington State discovered that commute times don’t change much when people move or switch jobs. The thinking is that if a person gets a new job that’s farther away, they are more likely to move. Plus, as people have moved to suburbia, some jobs have followed. It’s a two-way street. But that doesn’t mean employers can move to the burbs without consequences. If an employer moves and an employee doesn’t move as well, the employee is more likely to find another job. Companies looking to relocate simply to cut costs may find the high turnover that results more costly in the long run.

Commuting is a big part of our lives, so it makes perfect sense that it would affect so much of the world around us, especially the cities we live in. Take a dense city like New York that has oodles of jobs, and lots of dense housing close in. That density helps keep commute times reasonable. But somewhere like Tulsa that doesn’t have as many jobs doesn’t have as much need for density. Form follows function, and currently the freeways in Tulsa are functioning pretty well compared with New York.

That presents a real dilemma for urban planners, who have been striving to increase densities in cities across the board. One approach has been mixed-use development that blends retail, housing, and office space. That may help reduce trip times for errands and such, but it doesn’t preclude people from living in one mixed-use neighborhood and working in another. The reality is, we’re probably not going to change commute times. If we offer faster and better transportation, people will use it until it becomes overburdened. At which point they’ll just move closer to work. Attempts to influence urban form through design may not have much of an impact if jobs don’t follow.

Sources:

Cervero, R. (1996). Jobs-Housing Balance Revisited: Trends and Impacts in the San Francisco Bay Area, Journal of the American Planning Association, 62 (4) 511. DOI: 10.1080/01944369608975714

Cervero, R. & Duncan, M. (2006). ‘Which Reduces Vehicle Travel More: Jobs-Housing Balance or Retail-Housing Mixing?, Journal of the American Planning Association, 72 (4) 490. DOI: 10.1080/01944360608976767

Clark, W.A.V. & Davies Withers, S. (1999). Changing Jobs and Changing Houses: Mobility Outcomes of Employment Transitions, Journal of Regional Science, 39 (4) 673. DOI: 10.1111/0022-4146.00154

Clark, W.A.V., Huang, Y. & Withers, S. (2003). Does commuting distance matter?, Regional Science and Urban Economics, 33 (2) 221. DOI: 10.1016/S0166-0462(02)00012-1

Giuliano, G. & Small, K. (1993). Is the Journey to Work Explained by Urban Structure?, Urban Studies, 30 (9) 1500. DOI: 10.1080/00420989320081461

Levinson, D.M. (1997). Job and housing tenure and the journey to work, The Annals of Regional Science, 31 (4) 471. DOI: 10.1007/s001680050058

Schwanen, T., Dieleman, F.M. & Dijst, M. (2004). The Impact of Metropolitan Structure on Commute Behavior in the Netherlands: A Multilevel Approach, Growth and Change, 35 (3) 333. DOI: 10.1111/j.1468-2257.2004.00251.x

Schwanen, T. & Dijst, M. (2002). Travel-time ratios for visits to the workplace: the relationship between commuting time and work duration, Transportation Research Part A: Policy and Practice, 36 (7) 592. DOI: 10.1016/S0965-8564(01)00023-4

Vandersmissen, M.H., Villeneuve, P. & Thériault, M. (2003). Analyzing Changes in Urban Form and Commuting Time∗, The Professional Geographer, 55 (4) 463. DOI: 10.1111/0033-0124.5504004

Wachs, M., Taylor, B., Levine, N. & Ong, P. (1993). The Changing Commute: A Case-study of the Jobs–Housing Relationship over Time, Urban Studies, 30 (10) 1729. DOI: 10.1080/00420989320081681

Photo by Jekkone.

Urbanites leave the car behind, but not as often as you might think

Drive a lot? Housing density may not be to blame

If the world’s population lived like…

Shortly after I started Per Square Mile, I produced an infographic that showed how big a city would have to be to house the world’s 7 billion people. There was a wrinkle, though—the city’s limits changed drastically depending on which real city it was modeled after. If we all lived like New Yorkers, for example, 7 billion people could fit into Texas. If we lived like Houstonians, though, we’d occupy much of the conterminous United States.

Here’s that infographic one more time, in case you haven’t seen it:

What’s missing from it is the land that it takes to support such a city. In articles and comments about my infographic, some people overlooked that aspect—either mistakenly or intentionally. They shouldn’t have. Cities’ land requirements far outstrip their immediate physical footprints. They include everything from farmland to transportation networks to forests and open space that recharge fresh water sources like rivers and aquifers. And more. Just looking at a city’s geographic extents ignores its more important ecological footprint. How much land would we really need if everyone lived like New Yorkers versus Houstonians?

It turns out that question is maddeningly difficult to answer. While some cities track resource use, most don’t. Of those that do, methodologies vary city to city, making comparisons nearly impossible. Plus, cities in most developed nations still use a shocking amount of resources, regardless of whether they are as dense as New York or as sprawling as Houston. Any comparison of the cities in my original infographic would be an exercise in futility at this point.

But what we can do is compare different countries and how many resources their people—and their lifestyles—use. For countries, the differences are far, far greater than for cities. Plus, there’s a data set that allows for reliable comparisons—the National Footprint Account from the Global Footprint Network. Their methodology is based on peer-reviewed research by Mathias Wackernagel, the organization’s founder. It’s consistent and comprehensive. Each country’s footprint is assembled from sub-footprints, ranging from cropland to carbon to urbanization to fishing grounds. For my purposes, I used only terrestrial sub-footprints. I’ll let the results speak for themselves.

If the world's population lived like...

Sources:

Global Footprint Network. 2011. National Footprint Accounts, 2011 Edition.

Wackernagel, M., Kitzes, J., Moran, D., Goldfinger, S. & Thomas, M. (2006). The Ecological Footprint of cities and regions: comparing resource availability with resource demand, Environment and Urbanization, 18 (1) 112. DOI: 10.1177/0956247806063978

7 billion

Spare or share? Farm practices and the future of biodiversity

Africa’s urban quandary

Ethiopian market

I’ve heard the statistics so often they’re almost cliché: Fifty percent of the world’s population now lives in cities, and by 2050 it will be 70 percent. Yet those numbers fail to capture the enormity of the change, especially so for those of us in the developed world where for decades the majority of the population has lived in cities.

Urban growth is going to be especially taxing in Africa, where the population is expected to more than double by 2050 and urban populations are expected to triple. Furthermore, 70 percent of the urban population growth is predicted to occur in cities with less than 500,000 people today.

Such a demographic shift is occurring today in China, but the situation there is different than in Africa. China’s semi-command economy and authoritarian government make managing mass migrations easier. Furthermore, the Asian nation is two times bigger than Africa’s two largest nations—Algeria and the Democratic Republic of the Congo—combined. Planning on that scale has its advantages.

China’s and Africa’s circumstances aren’t entirely dissimilar, though. China’s expanding cities have displaced farmers on the periphery, leading to protests. Social strife in African nations is similarly problematic. Take the example of Bahir Dar, Ethiopia. Researchers from Tattori University in Japan and Mekelle University in Ethiopia mapped the city’s expansion from 1957 to 2009 and found that Bahir Dar’s area expanded 31 percent annually, or 88 hectares (217 acres) per year. That’s a shockingly rapid pace, even outpacing some of China’s cities.

It also portends social strife. The researchers interviewed 271 of the nearly 2,900 households whose farms had been seized between 2004 and 2009 to make way urban development. What they heard paints a gloomy picture. First the good news: Nearly all were offered and received monetary compensation. Now the bad: Nearly all of those who had received compensation said it wasn’t nearly enough to replace what they had lost. One farmer’s response explained the shortfall in a nutshell: “I had 300 eucalyptus trees, 45 coffee trees, ten mangos and avocados, and ten papayas on my land, but finally I received compensation only for the farmland.”

Even if monetary compensation were sufficient, it wouldn’t be what expropriated farmers need to transition to urban life. Nearly 60 percent of the surveyed households let their money sit in the bank—they hadn’t a clue what to do with it. “It would have been better to change the money into other assets. But to do this, I do not have experience and knowledge since I am illiterate,” one respondent said. A few were given other opportunities—40 percent were offered a line of credit and 24 percent were offered some sort of training. But those promises were often reneged.

The loss of farms isn’t just a tragedy for the affected families—residents of Bahir Dar will feel the effects, too. Though African cities are entering global food markets, many people still rely on outlying farms. And as cities expand, many of those farms disappear. That means crops have to be trucked greater distances, increasing food prices and further sensitizing them to rising oil prices. People in developing nations already pay a greater proportion of their income on food than those of us in developed nations. Any increases in food prices can be calamitous, as we saw in 2007 and 2008.

It doesn’t look like there is relief in sight, either. In Bahir Dar’s case, the researchers predict the city will double in extent by 2024. Similar patterns are likely to be seen across Africa as many cities will double in population by that date. As in developed countries, part of the solution will be better education and training for the displaced and newly immigrated. But given the projected magnitude of urban growth in Africa, even that may not be enough.

Source:

Haregeweyn, N., Fikadu, G., Tsunekawa, A., Tsubo, M., & Meshesha, D. (2012). The dynamics of urban expansion and its impacts on land use/land cover change and small-scale farmers living near the urban fringe: A case study of Bahir Dar, Ethiopia Landscape and Urban Planning DOI: 10.1016/j.landurbplan.2012.02.016

Photo by Marc Veraart.

Spare or share? Farm practices and the future of biodiversity

Salvaging disturbed forests may not save biodiversity

The last settler’s syndrome

Log cabin

In my mind, my hometown will always be a city of 24,000 people. It’ll also be supported by three major manufacturing companies. And it’ll always have a certain, intangible something. Of course, today West Bend has 5,000 more residents despite the demise of all three manufacturers. And every time I return, that certain something isn’t quite the same either. It’s like waking from a dream I can’t entirely reconstruct.

Geographer Gilbert F. White would say I’ve got “last settler’s syndrome”. To me, the ideal West Bend is the city I remember from my childhood—really, from my middle school days when my friends and I explored every street in the city by bike. White would also say I’m not alone: “Each wants his particular town and country landscape to remain just as it was when he or she arrived. The most recent settler wants to be the last settler.”

One could argue that the settlement of the United States was driven in part by last settler’s syndrome, that the pioneer spirit is just a euphemism for the malady. Pioneers who saw their wilderness fill up with other settlers may have become disillusioned. The Ohio River Valley, for example, wasn’t the same after the first trees were felled. So people picked up and moved on. It instilled a distinctly American habit—moving west for new opportunities.¹ My own ancestors followed that well-worn path, moving from Ohio to Wisconsin in the late 1800s.

Seemingly everything in our lives is touched by the last settler’s syndrome, from our childhood homes to our neighborhoods to our favorite haunts. It can be a powerful, positive force—if John Muir hadn’t been afflicted by last settler’s syndrome, there probably wouldn’t be a Yosemite National Park. But last settler’s syndrome also can be problematic. Neighborhood quarrels can result when new transplants push for change. And while obstinacy can be good in some cases—Muir and Yosemite—it also can be a barrier.

Understanding the last settler’s syndrome—how it affects people, and more importantly, how it affects ourselves—can help us better understand where we live, whether that be cities, farms, or forests. It also can help explain why change is so accelerated these days: We’re a population that moves a lot. As of 2010, less than 60 percent of Americans lived in the state in which they were born, almost 30 percent were born in another state, and almost 13 percent were born in another country. How people defined “the way things were” used to evolve over generations. Today it’s on the order of years.

In an era of constant upheaval—where cities look nothing like they did a few years ago, let alone a few decades ago—we need to consciously disassemble our relationship with places and analyze them in parts. What should we keep? What should we change? What needs to change? It’s difficult to abandon the past, but the future will be nothing like we imagine. Things are going to change whether we like it or not.

Why else is California so populous? I kid, I kid. Or do I? ↩

Sources:

Nielsen, J. M., Shelby, B., & Haas, J. E. (1977). Sociological carrying capacity and the last settler syndrome Pacific Sociological Review, 20 (4), 568-581

U.S. Census. 2011. Lifetime Mobility in the United States: 2010.

White, Gilbert F. 1986. The Last Settler’s Syndrome. in Geography, Resources, and Environment: Volume 1. Robert W. Kates and Ian Burton, eds. The University of Chicago Press, Chicago.

Photo by anoldent.

Wilderness housing boom challenges conservation

The woods that were

Interview: Jon Christensen on California's cities

Gold L.A.

The U.S. Census released a report on urban population on Monday, and in it was a perhaps-unexpected fact: Of the ten most densely populated cities, seven of them are in California. Indeed, California’s showing was so strong that the great bastion of urbanism in the United States — the New York-Newark metro area — just barely made the top five.

John King, the San Francisco Chronicle’s urban design critic, interviewed a number of experts about California’s unique status. Among them was Jon Christensen, executive director of the Bill Lane Center for the American West at Stanford University. One of Christensen’s quotes caught my attention, so I followed up with him via email to explore why California is such a hotbed of urbanism. Our correspondence follows:

Tim De Chant: What’s special about California that it has so many dense urban areas?

Jon Christensen: The American West, in general, and California, in particular, is really a metropolitan region and has been for a long time. California, Nevada, Utah, and Arizona are among the 10 most urbanized states. The settlement pattern in the West is one of concentrated cities surrounded by wide open spaces — often substantially made up of public lands. This is true of California as well.

So it’s really the interplay of the history of cities and their hinterlands in the American West that explains why California has such dense urban areas. The fact that they are among the most dense urban areas in the country is also a result of population growth in California. The state has been and still is a great place for many people to live.

De Chant: In your chat with John King, you said, “It’s a legacy of how in our minds’ eye we have always separated California into ‘urban’ land and ‘productive’ land and then wilderness, the cathedrals of nature.” Do you think that mental dichotomy has played a role in how California urbanized?

Christensen: I actually think that the way we have urbanized and the creation of that mental division, which is really a legacy of John Muir’s vision of California, have both played crucial roles in how we think about cities in California. This, in turn, shapes the way that density is measured, of course. Take the San Francisco-Oakland urban area, which as it is measured by the Census includes the populated areas of Marin but not the open lands of the Golden Gate National Recreation Area just to the west.

If those lands were included in the San Francisco-Oakland area, the denominator for the equation of people per square mile would be bigger, and the measure of density would be lower. That wouldn’t change the fact that the city is still one of the most densely populated in the country. But it does miss the fact that we live in a very densely populated metropolitan region that also has ready access to conserved public lands practically at our doorsteps, or a short drive or bus or bike ride away.

De Chant: In other parts of the country, that distinction isn’t so clear. Has that played a role in sprawl?

Christensen: I’m not sure that the mental distinction has played as important a role as the existence of public lands. Of course, public lands are, in some ways and particularly in some cases, the products of intentional human agency, political organizing, and conservation movements. This is true of the Golden Gate National Recreation Area and much of the rest of the lands protected around the Bay Area, for example.

A strong conservation vision runs deeply through the history of the Bay Area as Richard Walker shows in his great book The Country in the City. That explains a lot, here. But it doesn’t necessarily explain Los Angeles, Phoenix, or Las Vegas. For that, we have to look at public lands that were never homesteaded and thus have, to varying degrees, constrained cities. We also have to look at geography and topography. The San Gabriel Mountains constrain Los Angeles even more than the coastal mountains constrain the Bay Area.

De Chant: In a tweet you said you think of California as “quite a mixed up rather than clearly divided landscape.” Why the divide between the California of our imaginations and the California of reality?

Christensen: I think we still live in John Muir’s California in our minds, a state divided between the cities, the productive landscapes of farming, ranching, and mining, and the wilderness cathedrals of the Sierra Nevada. I think that’s changing as we recognize that people have played a role in constructing, shaping, and changing nature from the city out through the countryside and even to the wilderness, and that nature runs through it all as well.

The focus on hybrid human and natural landscapes, novel ecosystems, and ecosystem services all point to the ways that our thinking about nature is changing. But it’s changing slowly. John Muir’s California is still a powerful vision. It’s just too simple to be very useful in thinking about the present, let alone the future.

De Chant: In much of California, nature never feels far away. Why is that?

Christensen: Because it never is far away. Because of geography, topography, the history of settlement, and a long history of conservation efforts, wild nature is close in to the city in much of California, sometimes right in the middle of the city. We’re also bringing nature back to the city, daylighting creeks, restoring the L.A. River, planting urban gardens. And we’re increasingly realizing that nature is in the city already. It never went away. And we need to be more cognizant of the processes of nature that flow through the city and of which the city is made if we are going to fashion more sustainable urban living here in California and around the world.

De Chant: There’s on old saying, “As goes California, so goes the nation.” Do you think that’s the case with urban development?

Christensen: I do think that we have many useful things to share with the nation and the world from our history and experience. And from our current efforts to understand and shape nature in our metropolitan regions—in San Francisco, but even more so in Los Angeles, which is truly a global city in so many ways and the most densely populated city in the United States, as it happens.

But I don’t think it’s a simple matter of “as goes California, so goes the nation” or the world. Differences are important, whether they are historical, geographic, political, economic, cultural, or other differences. I think there are many similarities between cities in the United States and around the world, which makes me think that vocabularies, rules of thumb, lessons even, could be transferable. But they will have to be adapted to different cities, by the people making those cities.

De Chant: How do we transfer those lessons learned in California to other places?

Christensen: Your saying that “as goes California, so goes the nation” does get at a historical reality that California has been a site of innovations in ideas, technologies, policies that have influenced the nation and the world. And our dense cities in the San Francisco Bay Area and Los Angeles have also been key nodes in global networks of ideas, commerce, technology, and even species. The eucalyptus and palm are iconic examples. So I think the lessons will spread. But I also think it’s imperative that we speed up the process.

Over roughly the next two generations the urban population on the planet will double, and the urban built environment will have to double. How that happens will dramatically shape the future of how human beings live together and live with nature on Earth.

I don’t have answers, and I’m eager to learn, but I think we can start by mining our rich, diverse history and experience of thinking about and doing conservation and development together, in relationship to each other, over time in our cities, to come up with some common vocabularies, ways of speaking about this relationship, and rules of thumb, basic guides to planning and constructing hybrid human and natural cities, that can be adapted to different circumstances in different places. Then we need to figure out how to share these conceptual tools with the people who are actually going to build the cities of the future soon.

Photo by Neil Kremer.

For metros, two cities can be better than one

Map of photos taken in Minneapolis and St. Paul, Minnesota

Cities were, for thousands of years, distinct and easily identifiable entities. You were either in the city or in the country. Medieval cities took this to the extreme, building walls to make explicit the distinction. Johann Heinrich von Thünen systematized the idea in 1826 when he sketched a hypothetical map that, when simplified, looked like a bow-and-arrow target. The city sat in the center and was surrounded by rings of successively less valuable farmland. It was all very orderly and very German. And for a while it did a good job describing the relationship between the city and the hinterland.

Then came the railroads and automobiles that shot holes through von Thünen’s well-organized bullseye. And in places where two cities were less than a few dozen miles apart, even the boundary between the two became blurred. Today, it’s not uncommon to find metropolitan areas with two, three, even four major cities anchoring them.

Von Thunen's model of land use

Multi-city metros would seem to be a many-headed monster, riddled with contrary opinions and paralyzed by indecision. But that doesn’t alway seem to be the case. As far as labor productivity is concerned, multi-city metros—or polycentric metros, as the literature calls them—may have a distinct advantage. A study of all metropolitan areas in the United States with populations above 250,000 by Evert Meijers and Martijn Burger shows that productivity is higher in metros with more than one city. The effect is especially pronounced among smaller metro areas.

Meijers and Burger speculate that’s because smaller cities tend to have smaller problems—less traffic, lower crime rates, and so on. By splitting the problems up among a few cities, polycentric metros can host a large population without experiencing the problems of a similarly sized, monocentric metro.

But the advantages of multi-city metros diminish as the entire area’s population grows. It’s as though the larger entity needs one place to focus its efforts. So a metro area with two cities, each one-half the size of London, wouldn’t necessarily be more productive than London itself.

Multi-city metros also fall short on other critical parts of city life—cultural and leisure opportunities. Cultural outposts like opera houses and art museums benefit greatly from larger populations, which typically contain more benefactors, both wealthy and otherwise. The same goes for sports teams. Every city would like one for themselves. Say Ft. Worth wants to build an art museum. It’s probably not going to attract some donors from Dallas, who would rather see one built in their city. Chicago doesn’t have such a problem. Monocentric metros don’t have to worry about sharing.

As cities’ borders swell, multi-city urban agglomerations are probably going to be more and more common. Even within existing metropolitan areas, smaller cities could rise to prominence. Minneapolis and St. Paul, for example, have had to contend with the rise of Bloomington. The key will be for leaders to learn to work together, coordinating efforts rather than stepping on each other’s toes.

Sources:

Meijers, E. (2008). Summing Small Cities Does Not Make a Large City: Polycentric Urban Regions and the Provision of Cultural, Leisure and Sports Amenities Urban Studies, 45 (11), 2323-2342 DOI: 10.1177/0042098008095870

Meijers, E., & Burger, M. (2010). Spatial structure and productivity in US metropolitan areas Environment and Planning A, 42 (6), 1383-1402 DOI: 10.1068/a42151

Map of the Twin Cities by the inimitable Eric Fischer.

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Why New York City keeps getting bigger

New York City skyline

Q: Why is New York City the most populous city in the United States?

A. Because it was America’s most populous city in 1900.

Q. Why was New York City America’s most populous city in 1900?

A. Because it was America’s most populous city in 1800.

History seems to be protecting New York City’s status as the most populous city in the United States. Indeed, Paul Krugman has suggested that accidents of history gave New York City a leg up on others, and that once favored it grew into the metropolis we know today. But New York is not alone. Since 1840, the densest American cities have not only grown substantially, they also represent a larger share of the American population. The same can be said of other world cities, too. They are like snowballs—they’re big and they keep on getting bigger.

But how big cities gained the upper hand is not necessarily an accident, as Krugman’s use of the word might suggest. What has helped them grow so large is actually a specific set of geographic characteristics—location near an ocean or river (or better, both), mild climate, and ready access to natural resources. City founders may not have been working off a checklist, but they knew where to site their settlements to make the most of their surroundings.

It’s no surprise that prosperous cities are often located near large bodies of water. Water is the cheapest way to move goods, and was even more so before the Industrial Revolution. Access to navigable water meant food and raw materials could be easily brought to market and goods manufactured in the city could be cheaply exported. Water facilitated the movement of ideas, too. Both New York City and San Francisco, for example, benefitted from their status as major gateways for immigration. Immigrants were not merely a source of labor—they brought with them a diversity of ideas. Eventually, the importance of water subsided as railroads and interstate highways were built. Yet cities that were founded on coastlines or rivers continued to dominate.

Their size was the secret to their success. One of Krugman’s important early contributions was a model that showed how an already large city could grow to dominate the region. His theory was really nothing new—Johann Heinrich von Thünen described nearly the same thing in 1826—but Krugman translated the concept into today’s mathematical vernacular. Other researchers quickly picked up the thread and dug out real-world evidence of the snowball effect, including one study that looked at population growth in nearly 800 American counties between 1840–1990. It found that not only did the biggest cities grow during that time, they grew at a faster rate than other cities. New York grew more than the rest because it was bigger than the rest.

Today, New York’s fate doesn’t depend on the ocean or the river, but it does owe its status to their confluence. Its geographic past continues to steer its future. I’m tempted to haul out a favorite phrase of mine—ghosts of geography—but these cities aren’t really ghosts. They’re are very much alive. Oceans and rivers may not be as relevant to today’s world cities as they once were, but without them, many cities wouldn’t be as successful. From that perspective, it seems less likely that the founders of New York, London, and Tokyo stumbled on a happy accident and more likely that they had a keen understanding of geography.

Sources:

Ayuda, M., Collantes, F., & Pinilla, V. (2009). From locational fundamentals to increasing returns: the spatial concentration of population in Spain, 1787–2000 Journal of Geographical Systems, 12 (1), 25-50 DOI: 10.1007/s10109-009-0092-x

Beeson, P. (2001). Population growth in U.S. counties, 1840–1990 Regional Science and Urban Economics, 31 (6), 669-699 DOI: 10.1016/S0166-0462(01)00065-5

Gibson, Campbell. 1998. Population of the 100 largest cities and other urban places in the United States: 1790 to 1990. U.S. Bureau of the Census, Population Division Working Paper No. 27.

Krugman, P. (1991). Increasing Returns and Economic Geography Journal of Political Economy, 99 (3) DOI: 10.1086/261763

Photo by Greg Knapp.

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Population density and the evolution of ownership

Lamborghini Aventador in traffic

Yours. Mine. Even a two year-old can understand the basics of ownership. Those two words are also freighted with meaning, implying volumes about resources, control, privilege, and social standing. But what they don’t say is why it is we care so much about who owns what.

There are a number of possible reasons for why we value our possessions and covet those of others. True to form, I found one paper that suggests that population density may be responsible for the evolution of ownership. It’s a game theoretic study by Japanese behavioral scientist Shiro Horiuchi in which he uses an established mathematical model—the Hawk-Dove-Bourgeois game—to sift through the possible origins of possession in both animals and humans.

The Hawk-Dove-Bourgeois game (HDB) is a modification of the classic Hawk-Dove game. In addition to the two existing player types—hawks, who fight to acquire resources or territory and viciously defend what’s theirs, and doves, who avoid conflict at all costs—HDB adds a third strategy, called bourgeois. Bourgeois are a bit of a hybrid of the two existing approaches. A bourgeois player, when challenged for ownership, will fight furiously to keep it. But unlike hawks, they won’t attack other players to acquire resources.

Horiuchi took this game and threw out the standard dove and bourgeois strategies, replacing them instead with strong and weak bourgeois. Weak bourgeois are more similar to doves, which means they are less likely to engage in conflicts. Strong bourgeois can adopt a hawk- or dove-like stance depending on their territorial boundaries: If the contested area is within their boundaries, they’ll fight like hawks. If not, they’ll sit out like doves. Players can change strategies depending on how well they are doing relative to their neighbors. The goal is to control 10 units of territory.

In layman’s terms, the strong bourgeois strategy is a proxy for ownership in its purest sense—strong bourgeois players only fight to retain what’s theirs; anything else and they abstain from conflict. And what emerged from the games was a clear picture of strong bourgeois dominance at higher population densities. That doesn’t mean strong bourgeois players controlled more territory—remember, they were limited to a maximum of 10 units. Rather it means that more players adopted that strategy, judging that it was the best way to obtain and hold the maximum territory, especially as the playing field became more crowded.

Previous studies that used the unmodified HDB game didn’t come to the same conclusion, arguing that the bourgeois strategy—ownership, in other words—isn’t advantageous when resources are high. But those findings are refuted by real world studies of primates that show groups are willing to defend resource-rich home ranges, Horiuchi points out. His modifications and results more closely match the empirical data and suggest that ownership not only arises as population densities increase, but that it’s the best way to succeed.

As an ecologist, this result did not surprise me. In ecology, resources are everything. Even organisms as sedate as plants compete ferociously for resources, employing competitive tactics that range from rapid growth to chemical warfare. But in modern, developed societies where the bare necessities are frequently met, I wondered how these findings might apply. I ran Horiuchi’s result past a friend of mine who is a social psychologist, and he indicated that ownership today is not merely about resources, but status. Controlling more territory—or even just expressing one’s wealth in ever more ostentatious ways through possessions—is just another way in which the strong bourgeois strategy could continue to exert its influence, even though we’re not struggling to survive.

Frankly, I’m not surprised. Based on anecdotal observations of the various places I’ve lived, possessions appear to play a larger role in people’s lives the denser and more populous a city becomes. In large cities, people who earn double their peers seem more inclined to flaunt that wealth compared with the same individuals in smaller towns. The social psychological explanation makes sense in this case. It’s harder to stand out in denser, more populous places, which may lead to more conspicuous consumption.

Source:

Horiuchi, S. (2007). High population density promotes the evolution of ownership Ecological Research, 23 (3), 551-556 DOI: 10.1007/s11284-007-0408-6

This is your brain in the city

Income inequality in the Roman Empire

Agrippina the Younger

Over the last 30 years, wealth in the United States has been steadily concentrating in the upper economic echelons. Whereas the top 1 percent used to control a little over 30 percent of the wealth, they now control 40 percent. It’s a trend that was for decades brushed under the rug but is now on the tops of minds and at the tips of tongues.

Since too much inequality can foment revolt and instability, the CIA regularly updates statistics on income distribution for countries around the world, including the U.S. Between 1997 and 2007, inequality in the U.S. grew by almost 10 percent, making it more unequal than Russia, infamous for its powerful oligarchs. The U.S. is not faring well historically, either. Even the Roman Empire, a society built on conquest and slave labor, had a more equitable income distribution.

To determine the size of the Roman economy and the distribution of income, historians Walter Schiedel and Steven Friesen pored over papyri ledgers, previous scholarly estimates, imperial edicts, and Biblical passages. Their target was the state of the economy when the empire was at its population zenith, around 150 C.E. Schiedel and Friesen estimate that the top 1 percent of Roman society controlled 16 percent of the wealth, less than half of what America’s top 1 percent control.

To arrive at that number, they broke down Roman society into its established and implicit classes. Deriving income for the majority of plebeians required estimating the amount of wheat they might have consumed. From there, they could backtrack to daily wages based on wheat costs (most plebs did not have much, if any, discretionary income). Next they estimated the incomes of the “respectable” and “middling” sectors by multiplying the wages of the bottom class by a coefficient derived from a review of the literature. The few “respectable” and “middling” Romans enjoyed comfortable, but not lavish, lifestyles.

Above the plebs were perched the elite Roman orders. These well-defined classes played important roles in politics and commerce. The ruling patricians sat at the top, though their numbers were likely too few to consider. Below them were the senators. Their numbers are well known—there were 600 in 150 C.E.—but estimating their wealth was difficult. Like most politicians today, they were wealthy—to become a senator, a man had to be worth at least 1 million sesterces (a Roman coin, abbreviated HS). In reality, most possessed even greater fortunes. Schiedel and Friesen estimate the average senator was worth over HS5 million and drew annual incomes of more than HS300,000.

After the senators came the equestrians. Originally the Roman army’s cavalry, they evolved into a commercial class after senators were banned from business deals in 218 B.C. An equestrian’s holdings were worth on average about HS600,000, and he earned an average of HS40,000 per year. The decuriones, or city councilmen, occupied the step below the equestrians. They earning about HS9,000 per year and held assets of around HS150,000. Other miscellaneous wealthy people drew incomes and held fortunes of about the same amount as the decuriones.

In total, Schiedel and Friesen figure the elite orders and other wealthy made up about 1.5 percent of the 70 million inhabitants the empire claimed at its peak. Together, they controlled around 20 percent of the wealth.

These numbers paint a picture of two Romes, one of respectable, if not fabulous, wealth and the other of meager wages, enough to survive day-to-day but not enough to prosper. The wealthy were also largely concentrated in the cities. It’s not unlike the U.S. today. Indeed, based on a widely used measure of income inequality, the Gini coefficient, imperial Rome was slightly more equal than the U.S.

The CIA, World Bank, and other institutions track the Gini coefficients of modern nations. It’s a unitless number, which can make it somewhat tricky to understand. I find visualizing it helps. Take a look at the following graph.

Gini coefficient of inequality

To calculate the Gini coefficient, you divide the orange area (A) by the sum of the orange and blue areas (A + B). The more unequal the income distribution, the larger the orange area. The Gini coefficient scales from 0 to 1, where 0 means each portion of the population gathers an equal amount of income and 1 means a single person collects everything. Schiedel and Friesen calculated a Gini coefficient of 0.42–0.44 for Rome. By comparison, the Gini coefficient in the U.S. in 2007 was 0.45.

Schiedel and Friesen aren’t passing judgement on the ancient Romans, nor are they on modern day Americans. Theirs is an academic study, one used to further scholarship on one of the great ancient civilizations. But buried at the end, they make a point that’s difficult to parse, yet provocative. They point out that the majority of extant Roman ruins resulted from the economic activities of the top 10 percent. “Yet the disproportionate visibility of this ‘fortunate decile’ must not let us forget the vast but—to us—inconspicuous majority that failed even to begin to share in the moderate amount of economic growth associated with large-scale formation in the ancient Mediterranean and its hinterlands.”

In other words, what we see as the glory of Rome is really just the rubble of the rich, built on the backs of poor farmers and laborers, traces of whom have all but vanished. It’s as though Rome’s 99 percent never existed. Which makes me wonder, what will future civilizations think of us?

Source:

Scheidel, W., & Friesen, S. (2010). The Size of the Economy and the Distribution of Income in the Roman Empire Journal of Roman Studies, 99 DOI: 10.3815/007543509789745223

Photo by Biker Jun.

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Ghosts of ecology

Population density fostered literacy, the Industrial Revolution

Ghosts of geography

Population density fostered literacy, the Industrial Revolution

Without the Industrial Revolution, there would be no modern agriculture, no modern medicine, no climate change, no population boom. A rapid-fire series of inventions reshaped one economy after another, eventually affecting the lives of every person on the planet. But exactly how it all began is still the subject of intense debate among scholars. Three economists, Raouf Boucekkine, Dominique Peeters, and David de la Croix, think population density had something to do with it.

Their argument is relatively simple: The Industrial Revolution was fostered by a surge in literacy rates. Improvements in reading and writing were nurtured by the spread of schools. And the founding of schools was aided by rising population density.

Unlike violent revolutions where monarchs lost their heads, the Industrial Revolution had no specific powder-keg. Though if you had to trace it to one event, James Hargreaves’ invention of the spinning jenny would be as good as any. Hargreaves, a weaver from Lancashire, England, devised a machine that allowed spinners to produce more and better yarn. Spinners loathed the contraption, fearing that they would be replaced by machines. But the cat was out of the bag, and subsequent inventions like the steam engine and better blast furnaces used in iron production would only hasten the pace of change.

This wave of ideas that drove the Industrial Revolution didn’t fall out of the ether. Literacy in England had been steadily rising since the 16^th century when between the 1720s and 1740s, it skyrocketed. In just two decades, literacy rose from 58 percent to 70 percent among men and from 26 percent to 32 percent among women. The three economists combed through historical documents searching for an explanation and discovered a startling rise in school establishments starting in 1700 and extending through 1740. In just 40 years, 988 schools were founded in Britain, nearly as many as had been established in previous centuries.

The reason behind the remarkable flurry of school establishments, the economists suspected, was a rise in population density in Great Britain. To test this theory, they developed a mathematical model that simulated how demographic, technological, and productivity changes influenced school establishments. The model’s most significant variable was population density, which the authors’ claim can explain at least one-third of the rise in literacy between 1530 and 1850. No other variable came close to explaining as much.

Logistically, it makes sense. Aside from cost, one of the big hurdles preventing children from attending school was proximity. The authors’ recount statistics and anecdotes from the report of the Schools Inquiry Commission of 1868, which said boys would travel up to an hour or more each way to get to school. One 11 year old girl walked ten miles a day for her schooling.

Many people knew of the value of an education even in those days, but there were obvious limits to how far a person could travel to obtain one. Yet as population density on the island rose, headmasters could confidently establish more schools, knowing they could attract enough students to fill their classrooms. What those students learned not only prepared them for a rapidly changing economy, it also cultivated a society which valued knowledge and ideas. That did more than just help spark the Industrial Revolution—it gave Great Britain a decades-long head start.

Sources:

Boucekkine, R., Croix, D., & Peeters, D. (2007). Early Literacy Achievements, Population Density, and the Transition to Modern Growth Journal of the European Economic Association, 5 (1), 183-226 DOI: 10.1162/JEEA.2007.5.1.183

Stephens, W. (1990). Literacy in England, Scotland, and Wales, 1500-1900 History of Education Quarterly, 30 (4) DOI: 10.2307/368946

Hunter-gatherer populations show humans are hardwired for density

Do people follow trains, or do trains follow people? London’s Underground solves a riddle

Photo scanned by pellethepoet.

7 billion

Sometime today—or maybe it’s already happened—the 7 billionth person on this planet will be born. It’s a milestone, that’s for certain, though I’m unsure whether it’s auspicious or portentous. What I do know is it’s a bit contrived. The 7 billionth person will face the same challenges as the baby born just before or just after. They are all entering a world that is trying to answer its most pressing question—how many of us can it support?

The answer depends, of course, on what sort of future those people will have. Will they live like Americans—sated and safe—or like Somalians—as uncertain about their next meal as they are about their country’s fate? That, of course, depends on resources. In truth, we won’t know the answers to any of these questions until we get there, if we’re even lucky enough to realize when we’ve arrived.

For years now, I’ve felt as though the world has been filling up around me. Part of that has been the result of changing scenery, an impression reinforced by years of moving up the density ladder from small towns to bigger cities. But that feeling is also supported by cold, hard facts. My worlds are filling up. It’s most evident in my hometown, a small city where change comes slowly if at all. Yet even there, the roads and houses and shops I knew can’t contain the now pulsing masses, grown half again as large as when I first knew them. Like a teenager, the city is coping with its new size awkwardly. Ambivalent about the future, it keeps trying to be the city I knew. But even I—with my propensity for nostalgia—know better. Every time I return, as I sit trapped a dozen deep at a stoplight, a lesson is writ large in the taillights of the car in front of me. Growth, like progress, cannot be stopped.

So as we cross this synthetic threshold, close your eyes for a second to take snapshot of the world as it is. It will never be the same. Then open them to a future that’s two people fuller.

Ghosts of geography

Density solidified early human domination

Sunset over the Kenyan savanna

It’s no surprise that Homo sapiens dominates the Earth. After all, we’re resourceful, social, and smart. No, the surprise is how we did so in just 50,000 years. Such a pace is unprecedented, especially for a long living, slow reproducing species such as ours. Intelligence and opposable thumbs certainly helped, but we aren’t the only ones who can use a tool or solve a puzzle. Rather, a peculiarity of our social nature may be what has set us apart, allowing us to live in nearly every biome on Earth.

The exact mechanics of how sociality fostered our dominance are fuzzy. Myriad archaeologists and anthropologists work hard to resolve those uncertainties, but history is vast and their resources are comparatively small. There is another option, though, one that relies on mathematical machinations and close study of the characteristics of modern day hunter-gatherer groups. Using those methods, a group of anthropologists and biologists think they may have solved part of the migratory riddle. Our predisposition to living densely, they suppose, may have contributed to our stunning success beyond the savannas of Africa.

A sublinear relationship between population size and home range size—meaning that larger groups live at higher densities—imparts special advantages for species that can deal with the twin burdens of density, overshoot and social conflict. Overshoot describes a population that overwhelms its habitat, devouring all available food and otherwise making a mess of the place. Social conflict is as it sounds, where tight proximities provoke fights between individuals. Together, those snags can bring a once booming population to it’s knees.

But social animals are uniquely adapted to cope with those problems. For one, social behavior soothes tensions when they do rise. And when it comes to the necessities of life, density conveys a distinct advantage for social species—resources, chiefly food, become easier to find. Larger, denser populations squeeze more out of a plot of land than an individual could on his or her own.

Density itself wasn’t directly responsible for the first forays out of Africa. Those groups were were too small and dispersed to receive a substantial boost from density. They faced the worst the natural world had to offer, and many probably couldn’t hack it.

Where population density conferred its advantages was when subsequent waves of colonizers followed. Density allowed those people to thrive. They joined the initial groups, growing more populous and drawing more resources from the land. This made groups more stable both physically and socially—full bellies lead to happier and healthier people. As each group’s numbers grew larger, their social bonds grew stronger and their chances of regional extinction plummeted. In other words, once people worked together to establish themselves, they were likely there to stay.

It’s a heartwarming story the scientific paper tells in the unsentimental language of mathematics. It implies that the essential success of our species can be boiled down to one variable, β, and one value of that variable, ¾. The variable β is an exponent that describes how populations scale numerically and geographically. Its value of ¾ is significant. When β equals one or greater, each additional person requires the same amount of land or more—the group misses out on density’s advantages. But when β is less than one—as it is in our case—then a population becomes denser as it grows larger.

The degree of our sociality has allowed us to bend the curve of population density in our favor. If early humans had been an entirely selfish species—each individual requiring as much or more land than the previous—β would be equal to one or greater. We wouldn’t have lived at higher densities as our populations grew, and early forays beyond the savanna might have petered out. Instead of conquering the globe, we’d have been a footnote of evolution.¹

And here is where we can consider how this affects our modern lives. Population density may have aided our sojourn out of Africa, but it’s clear there are limits. Hunter-gatherer populations appear to be limited to around 1,000 people, depending on the carrying capacity of the ecosystem. Technology has raised carrying capacities beyond that number—as evinced by the last few millennia of human history—but we don’t know it’s limits. A scaling exponent equal to ¾ may have helped our rise to dominance, but it also could hasten our downfall. Technology may be able to smooth the path to beyond 7 billion, but what if it can’t? What if ¾ is an unbreakable rule? What happens if we reach a point where density can no longer save us from ourselves?

—

¹ I might point out here that β=¾ could tell us something about the viability of libertarianism, but that’s a subject for another post.↩

Source:

Hamilton, M., Burger, O., DeLong, J., Walker, R., Moses, M., & Brown, J. (2009). Population stability, cooperation, and the invasibility of the human species Proceedings of the National Academy of Sciences, 106 (30), 12255-12260 DOI: 10.1073/pnas.0905708106

Photo by lukasz dzierzanowski.

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What do population density, lightning, and the phone company have in common?

Lightning strike in Tokyo

File this one under “applications of population density”. Researchers working for Nippon Telephone and Telegraph—better known as NTT—discovered they could use an area’s population density to predict telecommunications equipment failure due to lighting strikes.

Telecommunications is an expensive business. Like other infrastructure, it requires a lot of manpower and capital to expand and maintain. But unlike many other systems, telecommunications—especially cellular network technology—has been advancing at a breakneck pace, requiring equipment to be upgraded or replaced every few years to stay current. Furthermore, the equipment is both delicate and expensive. Something like a lightning strike can easily cost tens to hundreds of thousands of dollars to repair.

The NTT researchers were interested in predicting where lightning strikes would exact the most damage in coming years, especially since some climate models predict more severe weather, which can lead to more lightning. The study focused on three prefectures in Japan—Tokyo, Saitama, and Gunma—which represent a gradient of population density ranging from one of the most built-up urban environments to relatively sparse farmland. The prefectures also fall along a gradient of lightning intensity, with Gunma at the high end receiving 10 strikes per square kilometer and Tokyo at the low end receiving 3 strikes per square kilometer.

Using past data on lightning strikes, telecom equipment failures due to lightning strikes, and the 2005 Japanese census, they developed a model to describe how telecom equipment failures due to lightning correlate with population density. At first blush, I expected urban areas to receive the brunt of the impact—after all, they have loads more equipment than rural areas—but the results were just the opposite. Expensive circuitry and antennas were safer in urban Tokyo than they were in rural Gunma, even when the discrepancy in lightning strikes between the two regions was taken into account.

The authors offer two explanations for why telecom equipment is safer in urban areas. First, many of the copper lines that feed base stations and boxes run underground in cities, which lowers the induced voltage during a strike. Second, the equipment itself tends to be exposed to the elements in the country, either on the ground or perched atop telephone poles. In the city, most of it in encased in apartment buildings.

But there is another possible explanation they missed—the design of telecom networks and their relationship to population density. The evidence lies in their calculated coefficient that describes how population density can predict equipment failures due to lightning strikes. The coefficient is ¾, and if you’ve been reading this blog for a while, you’ll no doubt recognize that number. As an exponent, ¾ is powerful descriptor, explaining a variety of phenomenon ranging from how plant sizes influences population density to how human population density affects the density of place names.

In this case, ¾ seems to say less about the pattern of lightning strikes than it does about telecom network design and the differences between rural and urban infrastructure. Denser populations require more equipment, but not at a fixed rate. Cellular networks provide a good example. In rural areas, cell sizes are limited by area, not the number of users. It’s the opposite in the city—the more users, the smaller cells become. Therefore, phone companies can rely on fewer cells and less equipment per person in the city than in the country.

The relationship between infrastructure demands and population density could go a long way to explaining why there is a lower rate of equipment failure in denser areas—there’s simply less equipment per person in the city than in the country. But the fact that telecom infrastructure—and damage to it—appears to scale at the same power that describes an range of phenomena related to density and metabolism, well, that’s just too good to be a coincidence.

Sources:

X. Zhang, A. Sugiyama, & H. Kitabayashi (2011). Estimating telecommunication equipment failures due to lightning surges by using population density 2011 IEEE International Conference on Quality and Reliability (ICQR) , 182-185 : 10.1109/ICQR.2011.6031705

Photo by potarou.

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Hunter-gatherer populations show humans are hardwired for density

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This post originally appeared on Scientific American’s Guest Blog.

High density living seems like a particularly modern phenomenon. After all, the first subway didn’t run until 1863 and the first skyscraper wasn’t built until 1885. While cities have existed for thousands of years—some with population densities that rival today’s major metropolises—most of humanity has lived at relatively low densities until recently, close to the land and the resources it provided. Before farming, nearly everyone was directly involved in the day-to-day hunting and gathering of food, which required living at even lower densities. It would seem as though our current proclivity for high density living runs counter to our biological underpinnings, that density has been thrust upon us by the demands of modern life.

It’s easy to arrive at that conclusion, in part because density is a hot topic these days. More than 50 percent of the world’s population now lives in cities—a fact repeated so often it’s almost a litany. But reciting that phrase doesn’t reveal the subtle effects implied by the drastic demographic shift. People migrating from the countryside face untold challenges wrought by density. Cities are complex places, fraught with crime, diseases, and pollution. Yet cities are also places of great dynamism, creativity, and productivity. Clearly, the benefits outweigh the drawbacks or else cities would have dissolved back into the landscape.

The benefits of living close to other people are evident even to hunter-gatherers. Though their societies have changed over the millennia, studying characteristics of present-day hunter-gatherers can let us peer into the past. That’s what was done by three anthropologists—Marcus Hamilton, Bruce Milne, and Robert Walker—and one ecologist—Jim Brown. In the process, they seem to have discovered a fundamental law that drives human agglomeration. Though their survey of 339 present-day hunter-gatherer societies doesn’t explicitly mention cities, it does show that as populations grow, people tend to live closer together—much closer together. For every doubling of population, the home ranges of hunter-gatherer groups increased by only 70 percent.

The way home ranges scale with population follows a mathematical relationship known as a power law. Graphs of power laws bend like a graceful limbo dancer—sharply at the base and more gradually thereafter—toward one axis or another, depending on the nature of the relationship. They only straighten when plotted against logarithmic axes—the kind that step from 1 to 10 to 100 and so on. One variable, known as the scaling exponent, is responsible for these attributes.

Hunter-gatherer population size and home range (updated)

Fig. 1 Hunter-gatherer home ranges scale to the three-fourths power. Above are representations of three populations and the size of their home range according to this relationship.

To see how scaling exponents apply in the case of hunter-gatherer territories, let’s look at the range of possible values and what each would mean in terms of density. If the exponent were equal to one, then home ranges would scale linearly with population size—10 people would occupy 10 square miles and 100 people would occupy 100 square miles. If the exponent were 1.2, then a group of 100 would occupy 250 square miles. And if the exponent were 0.75, a group of 100 people will only occupy 32 square miles. This last one is what Hamilton and his co-authors found.

Their result is the average of 339 societies, and there’s a bit of heterogeneity within that statistic. Not every group has a perfectly “average” way of hunting and gathering. Some hunt more, some gather more. Some find food on land, others in the water. Where and how hunter-gatherers get their food has a large impact on how densely they live, causing the density exponent to deviate slightly or greatly from three-quarters. For instance, groups which derive more than 40 percent of their food from hunting require larger territories because prey is not always evenly distributed or easily found. Their home ranges scale to the nine-tenths power, indicating sparser living. Gatherers require less space—their home ranges’ scale at the 0.64 power—largely due to plants’ sedentary lifestyles.

Hunter-gatherer societies which draw food from the water lived more compactly, too. The home range of aquatic foragers was consistently smaller across the range of population sizes—their exponent was 0.78 versus terrestrial foragers’ 0.79. Hamilton and his colleagues suspect this is because food from rivers, lakes, and ocean shores is more abundant and predictable than comparable terrestrial ecosystems.

But no matter what types of food are consumed, the overall trend remains the same. Every additional person requires less land than the previous one. That’s an important statement. Not only does it say we’re hardwired for density, it also says a group becomes 15 percent more efficient at extracting resources from the land every time their population doubles. Each successive doubling in turn frees up 15 percent more resources to be directed towards something other than hunting and gathering. In other words, complex societies didn’t just evolve as a way to cope with high-density—they evolved in part because of high density.

Update: The figure in this post originally reported 10.8 sq km for a group of 50 people. It should have been 18.8 sq km. The figure has been updated.

Source:

Hamilton, M., Milne, B., Walker, R., & Brown, J. (2007). Nonlinear scaling of space use in human hunter-gatherers Proceedings of the National Academy of Sciences, 104 (11), 4765-4769 DOI: 10.1073/pnas.0611197104

Photo by Gruban.

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When it's too crowded to have kids

Density can have profound effects on fertility. Population biologists call this phenomenon density dependence, and they’ve witnessed it in everything from single-celled organisms to elephants. It can influence fertility positively—individuals are more likely to meet mates in dense populations—or negatively—increased stress or lower food availability may drive fertility rates down. But despite evidence of the phenomenon in the natural world, little has been said about the its role in declining human fertility rates.

The relative paucity of studies examining density dependence in humans may be due in part to our persisting belief (conscious or unconscious) that in the course of developing culture, we have isolated ourselves from natural forces. Many previous studies of fertility rates tended to overlook what biologists see in the wild.

One study did, though. A demographic survey of around 150 countries, it uncovered strong evidence that population density is driving down human fertility rates. The authors accounted for all the usual variables found in fertility studies—infant mortality, gross domestic product per capita, percentage of women in the workforce, female literacy, and degree of urbanization. While those oft studied factors all still play a role, population density stood out as a new addition.

The researchers found that people throughout the world tend to have fewer kids when population densities are high, a pattern that repeated itself over the course of forty years. There were a few outliers—Australia has low population densities and low fertility while the Maldives has the opposite—but population density remained significant even when variables like infant mortality and GDP per capita included.

Density dependence was apparent even in the number of children people wanted, hinting that the cause may be more than just environmental. The authors used the Eurobarometer survey to see if people’s desires were aligned with population density. By and large, they were. People in sparsely populated Scandinavian countries desired more children, while people in the Netherlands wanted fewer. There were outliers, of course. The Irish continue to want larger families than average, the Germans fewer.

The exact mechanisms at work are still unknown. Density could be making food scarcer, or stress could be reducing fertility biochemically. Pollution may also be to blame. The psychological effects of crowding might be lowering libidos. Economics could be another driver. After all, many things are more expensive in higher density areas, whether that be food, shelter, child care, and so on. The truth is, we just don’t know at this point. But what should be clear is that culture and society have not insulated us from the forces of nature.

Source:

Lutz, W., Testa, M., & Penn, D. (2007). Population Density is a Key Factor in Declining Human Fertility Population and Environment, 28 (2), 69-81 DOI: 10.1007/s11111-007-0037-6

Photo by Miguel Michán.

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