Category Archives: Population

Where children go hungry in the world

Every day, tens of millions of children go to school—or to bed—hungry. Not only does it take a toll on their studies, hindering their chances of a better life, it also stunts their growth and makes them more susceptible to illness and disease.

Scroll and click around the map to see where in the world children are underweight, which is defined as two standard deviations below the median of the NCHS/CDC/WHO International Reference Population. It’s a pretty good indicator of kids who are chronically hungry.

The data covers 1990-2002 and isn’t available for all regions (those that are unavailable appear blue on the map). The raw data was compiled by the Center for International Earth Science Information Network.

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Your carbon footprint may not be as low as you think

Tokyo buildings

High-density living—it’s an urbanist’s answer to climate change. Living close is a straightforward solution to a complex problem. One that’s probably a little too simplistic. While living in dense cities certainly does reduce your carbon footprint, the results may not be as dramatic as you suspect.

That’s according to a new research paper by Chris Jones and Dan Kammen, two University of California, Berkeley researchers who have extensively studied people’s carbon footprints. Their results show that moving from a carbon-heavy suburb to an ultra-dense city will only reduce your emissions by 35 percent on average. Yes, that’s a big number, but perhaps not as significant as we’re often led to believe. But fortunately lurking within their data is an even simpler—and maybe even more effective—way for metro areas to reduce their footprint.

Jones and Kammen have spent years honing their methodology for determining people’s carbon footprints. Jones is the lead scientist at the Renewable and Appropriate Energy Lab and Kammen is its director and a professor at the university. Together they’ve created one of the most detailed and accurate carbon footprint calculators available online. To develop that tool, they had to ask a lot of people a lot of questions about their lifestyles. With that experience, they’ve published a number of papers that lift the veil on our energy use, revealing which aspects of our lives produce the most greenhouse gas emissions.

Their latest paper is contains some seemingly unexpected results, all gleaned by modeling emissions for individual ZIP codes. For example, you might expect carbon footprint to fall commensurately with population density. After all, living in the boonies makes you pretty reliant on cars while living in the city frees you to take transit. But it isn’t so clear cut. People living far from cities and suburbs have fewer destinations and tend to buy less, driving down their overall footprint.

As population density increases, then, household carbon footprints rise initially, up to 3,000 people per square mile. After that point, emissions per household drop, though the trend isn’t linear, it’s logarithmic, which is to say it falls fast at first but then with plateaus.

Jones and Kammen found that the most carbon intensive places to live are about 15 to 45 miles from the center of the nearest major city.¹ Most households in these bands have higher incomes and more members, both of which are tightly coupled with carbon emissions in the U.S. Those households also have higher transportation footprints—50 percent more than city center households. Overall, suburbs account for half of the U.S.’s carbon footprint. Large cities contribute 30 percent.

No city can escape its suburbs. As long as people have the means and the desire, they’ll live in those sorts of places. So to reduce a metro area’s overall carbon footprint, Jones and Kammen say, you have to tailor solutions that will work for each region of the country and each part of the metro. To be successful, those solutions must work with people’s existing behaviors.

Take the suburbs, for example. “These locations are ideal candidates for a combination of energy efficient technologies, including whole home energy upgrades and solar photovoltaic systems combined with electric vehicles,” they write. Forcing someone to use transit changes their behavior, and people are resistant to that. But if you encourage them to use electric cars, that works within their existing behavior. It’s an easier sell.

The overall trend of population density and household footprints offers another option, too. Pushing densities above 3,000 people per square mile can lower emissions substantially. That’s the tipping point in Jones and Kammen’s curve. Beyond that, they declined sharply, but then plateau. In other words, to make an significant impact, we just have to live a little closer together.

  1. The lowest emission rural areas are on par with people living in some major cities, though the densest cities still have the smallest footprints per capita.

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How to save a dying city


Forty years ago, Detroit was doing pretty well. The auto industry was cranking, employment was high, wages were decent, and the city was packed. Today, well, not so much.

Forty years ago, Pittsburgh was doing pretty well. The steel industry was cranking, employment was high, wages were decent, and the city was packed. Today, well, it’s actually not doing so bad.

Both Rust Belt cities have a lot in common. They were heavily working class, and when manufacturing started moving overseas and automation encroached on what was left, people lost their jobs. When manufacturing jobs didn’t return, they left. Since 1970, Detroit has lost more than 45 percent of its population, Pittsburgh more than 43 percent. So what makes the two different?

Education, in a word. Today, a greater proportion of Pittsburgh’s residents have college or higher degrees compared with Detroit. That comparison comes by way of Dan Hartley, a Cleveland Federal Reserve economist, who crunched some numbers for four hard-hit Rust Belt cities—Detroit, Pittsburgh, Buffalo, and Cleveland—and arrived at some not-surprising conclusions. Though most of his analysis focuses on Cleveland, it was the disparities between Detroit and Pittsburgh that caught my eye.

In 1970, before the Rust Belt grew rusty, both cities were at the tops of their games. Median household income in Motor City was $46,438,¹ not far off from today’s nationwide median of about $51,000. For a working class city, that’s not bad. Pittsburgh was in good shape, too, with a median income of $37,477. Home prices were similarly competitive. In economic terms, both Detroit and Pittsburgh were typical American cities.

But over time the two diverged. By 2006, the year in which Hartley’s analysis is based, median household incomes were down 35 percent in Detroit but only off 10 percent in Pittsburgh. Home prices mimic that on a lesser scale, with Detroit up 9 percent and Pittsburgh up 13 percent. Where they differ is in education. In 1970, 6 percent of Detroit’s population had a college or higher degree. In 2006, just over 11 percent did. Pittsburgh, on the other hand, more than tripled its share, going from 9 percent in 1970 to over 31 percent in 2006.

In that time, the Steel City invested heavily in wooing healthcare companies and was reasonably successful at it. But that shift would have stumbled if the city hadn’t already had a strong educational foundation. Both Carnegie Mellon and the University of Pittsburgh are located in the city, providing plenty of local college grads looking for employment. Detroit has Wayne State, which is not a bad school at all, but it can’t compare with two, high-reputation schools like Carnegie Mellon or the University of Pittsburgh, which together have 12,500 more students than Wayne State.

If you look closely and in the right places, you quickly notice that education is the cornerstone of many booming cities and regions. Silicon Valley wouldn’t be what it is today without UC Berkeley or Stanford, and the Boston area wouldn’t be a hub of robotics if it wasn’t for MIT. If you want a thriving city, focus on education. I won’t say everything else is just details, but smart people have a way of figuring those out.

  1. All figures are in 2009 dollars.


Hartley, Dan. 2013. Urban Decline in Rust-Belt Cities. Economic commentary, Cleveland Federal Reserve Bank.

Photo by migee_castaneda

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How to keep the economy growing when our population is not


Zero population growth is a period in future human history that is both hoped-for and feared. If we don’t get to that point, the world could literally become overrun with humans, straining already taxed resources like fresh water and farmland to the breaking point. But with zero population growth, the global economy—heavily reliant on a young and expanding workforce—could collapse. No matter what we hope, according to projections by the United Nations, it’s likely that within the next century, the global population will level off or even shrink.

It’s a prospect that vexes demographers and economists alike, which is a sharp change from the 1960s, when we feared rampant population growth. Now, we fret over the opposite, and for good reason. While stabilizing or declining numbers will certainly ease the burden on the environment, no one knows how society will function in a future with fewer people. Globally, it’s never happened before. Locally, we’re starting to see it in some countries such as Japan, which has been stuck at about 127 million for the last decade. By 2045, it will drop to 105 million, and it’s already affecting Japan’s long-term thinking—some economists are questioning the need for the country’s proposed maglev system if there are fewer people to ride it.

There’s another, more fundamental problem that zero or negative population growth poses, though—the transfer of knowledge. We know that when people come together, they tend to create new technologies, skills, and knowledge. Cities are hubs of innovation, universities are great factories of scholarship, and even smaller groups can inspire people to create wonderful things. Perhaps more importantly, the number and strength of our connections are vital for passing knowledge on to others, two recent studies suggest. Without those connections, our society could fall rapidly behind. Fortunately, the research also suggests a way to escape the declining population trap.

Ed Yong, who covered the two studies for Nature News, pointed out that the papers provide independent validation of the idea that cultural knowledge is tightly correlated with group size and connectedness. They approach the problem from slightly different angles. The first study examined whether group size affected how well cultural tasks—in this case making an arrowhead or a fishing net—were passed down from one group to the next. In every instance, groups of eight or 16 performed significantly better than groups of two or four. Bigger groups also developed better and quicker ways of making the arrowheads.

The second study tested how interpersonal connections affected performance of a task, in this case either duplicating an image on a computer or recreating a series of knots used in rock climbing. In the drawing experiment, which tested the creation of knowledge, inexperienced people started off, going by trial and error. Later generations of participants could watch earlier people’s attempts and use that to hone their skills. Some were given the opportunity to observe five different attempts, others were only given the chance to see one. Those who had access to five examples recreated the drawings more accurately than those who could only see one.

The knot-tying experiment tested how cultural knowledge was maintained. The first generation of participants was trained by an instructor. Later generations watched footage of previous people tying the knots. Those who could watch five examples were twice as good at tying the knots as those who could only watch one example. The more connections, the more faithfully that knowledge was passed on.

Together, these two papers make a strong case for social savvy being the foundation of our complex culture. The first paper—the one with the arrowheads and fishing nets—confirms experimentally what many scientists suspected, that larger groups are both more proficient and more innovative. But the second study really intrigues me. It’s the one that, I believe, offers a way to keep our economy surging when our population begins to level off or decline.

The key to that is social connections. The more connected people were in either experiment of the second study, the better they performed, whether that be for maintaining knowledge or advancing it. Following that thread, it stands to reason that we can successfully decouple economic growth from population growth if social connections continue to increase. So even if our numbers decline, as long as our connections do not, we will at the very least be able to maintain our cultural knowledge and hopefully our standard of living.

To do that, we need to meet three challenges. First, the trend toward urbanization needs to continue. Cities foster connections between people, and the more people that live in cities, the more cultural knowledge we can maintain. Second, the internet needs to be everywhere. As the internet has taken hold, it has connected people in ways never before imagined. It’s now easier to access scholarly articles, stay in touch with friends and family, and partner with peers around the globe, all of which serve to maintain and increase our collective knowledge. Finally, as cities swell, we need to make sure they are physically connected as seamlessly as possible. Large cities can provide a wealth of opportunities, but no single city can offer them all. Being able to zip from one to the next will be vital for our cultural survival.¹

If we can meet those three challenges, and if social connections continue to multiply as population stabilizes or declines, then I think we’ll have a good chance of maintaining economic growth and raising standards of living.

  1. I would argue that this implies that Japan’s maglev system will be even more important if the population declines as is predicted. They’ll need more connections, not fewer.


Derex M., Beugin M.P., Godelle B. & Raymond M. (2013). Experimental evidence for the influence of group size on cultural complexity, Nature, DOI:

Muthukrishna M., Shulman B.W., Vasilescu V. & Henrich J. (2013). Sociality influences cultural complexity, Proceedings of the Royal Society B: Biological Sciences, 281 (1774) 20132511-20132511. DOI:

Photo by eioua

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The uncanny valley of commerce, and what it means for your community

■ target

Your grocery store. Google. Target. What do these three have in common? They all gather personal information, and they all do it—and I’m paraphrasing here—”to serve their customers better.” In the case of your grocery store, they profile your habits to get you in the store, to buy more things. Same with Target. Google mines your personal information to hit you with ads you’re more likely to click on. In each case the company is looking to make money off their knowledge of you. It’s not that different from the way business used to be run. With one big exception.

In the past, when you visited a store, you may have known the owner. The owner of the hardware store knew you were a repeat customer, so he may have given you a deal on a new drill, knowing you’d probably be back for screws, lumber, and glue. Or maybe the owner of the shoe store, which you’d been shopping at for years, would cut you a deal on your kid’s new sneakers. In each case, they wanted to keep you as a customer. Your repeat business ensured future revenue, which is more valuable than a few extra dollars today.

Big businesses know this, too. They know that repeat customers are among the most profitable—that’s why there are frequent flier programs, club memberships, and loyalty cards. But somewhere along the line, they also realized they were sitting on a treasure trove. With every signup, with every logged purchase, people gave away personal information that hinted at what kind of customer they were. Companies started to mine that data, looking for patterns that would reveal even more intimate details. Target is perhaps best at this among large retailers, famously predicting their customers’ pregnancies weeks before they even know.¹

And therein lies the problem. Massive databases of personal information allow companies to do the same things businesses did in the past—offer deals to loyal customers, personalize offerings, and so on—but they do so without any sort of meaningful relationship. “Steve” may be genuinely interested in your budding family. Target is not, except to sell you more diapers. These companies are able to do make personal offerings, but in such a way that it’s clear no human is behind them. Call it the uncanny valley of commerce.

In commerce, though, relationships matter. That’s part—a large part, I’d argue—of what makes us queasy about data mining. Personalized deals are one thing when someone you know is offering them. But in the absence of a person we know, we don’t know what’s behind the gesture. Without a personal relationship, we can’t trust that these companies have our best interests in mind.

Now, things weren’t all sunshine and daisies in the past. Small operators used to disappear in the middle of the night, absconding with their customers’ money.² And while personal relationships can keep some vendors in line, it holds little meaning for others. It’s true that big companies can be held more accountable in many circumstances, but that doesn’t mean we trust them any more. There’s a reason they’re called “faceless corporations.”

Massive multinationals exist because of economies of scale, which has been shifting our economy from one driven by small proprietors to one dominated by large companies. It’s also changing the relationship between seller and buyer. And just as economies of scale have transformed businesses, they’ve also fostered population growth. The two go hand-in-hand. Because we’re now so numerous, we’re easier to deal with in bulk than one-on-one. But I suspect that transformation is also subtly altering our communities, displacing some of the relationships that were built around proprietors and customers. It’s not clear to me what’s taking their place.

There will always be opportunities for small businesses. How many? We don’t know. But there are certain to be fewer. Personal relationships in commerce will continue to wane, and I’m guessing it’ll have an enormous impact on our lives, our finances, and our communities.

  1. Charles Duhigg exposed some of Target’s secrets in his book The Power of Habit, an excerpt of which you can read online.
  2. Though truth be told, the same thing can happen today. It’s called bankruptcy.

Photo by Mr. T in DC

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Human population density drives extinctions

mountain gorilla

Sometimes there are scientific studies that seem to confirm the obvious. To wit: The more people that live in an area, the more species that go extinct.

No matter how superfluous it seems, it’s good that scientists undertake these studies, if only to confirm our suspicions, rule out potential confounding variables, or simply make the phenomenon feel more real. All three are the case with the recent paper on population density and animal extinctions. Jeffrey McKee, an anthropologist at the Ohio State University, first published on the relationship back in the early 2000s, and his latest confirms some of his earlier results and predictions.

McKee and his colleagues constructed a few models and fed them data for various variables, including human population density, species richness, GDP, conservation status (vulnerable, endangered, critical, etc.), precipitation, temperature, and others. The first time they ran the model, back in the early 2000s with data for the year 2000, they discovered a very strong correlation between population density and threatened species and nothing else. A later refinement found the population density-conservation status link could be refined by including GDP per unit area. The latest run, published this month using data for the year 2010, not only confirmed the predictions made in 2000 about 2010, it refined the overall predictive power of the model.

This new paper forecasts out to 2050, and the outlook is grim. By 2020, an average growing nation can expect 3.3 percent more threatened mammal and bird species. By 2050, that rises to almost 11 percent. So if a country has 114 threatened mammal and bird species today, like the United States does, it can expect to have 118 by the end of the decade and 126 by 2050. All due to population growth.

Faced with those statistics, conserving biodiversity seems like a quixotic battle. Population growth is beginning to slow, but there’s no way to halt it completely and immediately. Yes, human population growth will level off eventually, but what can we do in the meantime? One answer is to protect high-biodiversity areas from development, though that’s easier said than done. The richness that makes many ecosystems so complex also makes them attractive to humans. If development is to take place in those areas—and I see no reason why it won’t—we’ll have to take special care to support its native species.

The other option is to be more conscientious about where we develop. It’s likely that there’s a middle ground where human impacts can be balanced against losses in biodiversity. Finding it will take forethought and a bit of planning, but as I’ve said before, we can’t just plan the land we’ll occupy, we also have to plan the land we won’t.

Photo by Daniel Coomber


McKee J., Chambers E. & Guseman J. (2013). Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species, Human Ecology, 41 (5) 773-778. DOI:

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How population density affects mortality

Dark city

If you want to live a long time, where should you reside, the city or the countryside? There are compelling arguments to be made for both. In the city, you could be the victim of a crime; in the country, an accident of man or nature could claim your life. Regardless of the various marks for and against, overall death rates are neither higher nor lower in the city than in the countryside.

But suicide rates are a different story. A couple of years ago, I covered the topic in some detail, drawing on three published studies. I discovered that suicide rates are higher in less populated areas for a couple of reasons. One is access to weapons—there tend to be more of them in the countryside, and they’re an awfully effective way to end a life. But more significant than that is one’s mental state. People with mental disabilities are more likely to take their own lives, and there is less access to mental health resources in less densely populated areas.

That’s not all, though. A new working paper published to by a motley crew—two insect ecologists, a systems scientist, and a theoretical physicist—adds a new wrinkle to the conundrum of mortality rates and population density. Like many other researchers, they found no overall link between mortality and population density. But once they limited their sample to young people, they saw rates of suicide and, to a lesser extent, accidental death skyrocket at lower population densities. Accidental deaths are somewhat easy to explain. In low-density areas of developed countries, driving is common, as is driving at high speeds. Accidents at higher speeds are more likely to be deadly, and young, inexperienced drivers are involved in more accidents. More puzzling, though, was what happened at higher densities. Above 777 people per square mile (300 per square kilometer), suicide rates flattened.

As a raw number, that’s not very high. A city with a population density that low is hardly a city. But a county or state at or above that number is dense, which is what the researchers used—U.S. counties, Japanese prefectures, French départements, and so on. The sort of places that have those population densities contain some real cities or metro areas—San Diego County in California and Denton County in Texas, which is part of the Dallas-Fort Worth metro area.

The reasons for this floor remain illusive. The researchers think social bonds may play a role, citing a “stay alive” effect that biologists see in lab-grown cell populations, where cells that don’t receive constant prods from companions commit suicide. Cities, they say, provide equivalent prods; it’s as though the mere fact of interacting with other people reminds you to stay alive. It’s an intriguing notion, but it’s obviously not a perfect analogy since some people can live for a very long time without constant prodding. Plus, none of the authors of the paper are sociologists or anthropologists—their conclusions are a bit speculative without some support from those fields. Maybe they’re looking for someone in one of those fields to collaborate. Currently, the paper is merely in working form, meaning it hasn’t been peer reviewed. The authors have put it out there so their peers can propose ways to improve it.

Regardless, the floor in suicide rates they’ve found is intriguing. There’s bad news and good news in that result. The bad news is that adding social bonds by increasing population density doesn’t seem to affect suicide rates. To have any effect on that, we’ll need more robust social services to catch the people in danger of slipping through the cracks. But the good news is that there doesn’t appear to be a point at which the trend reverses—massive cities do not, it appears, drive us to the brink.

Photo by nosha.


Wang, Lei, Yijuan Xu, Zengru Di, and Bertrand M. Roehner. 2013. “How are mortality rates affected by population density?” arXiv: 1306.5179v1

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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.

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

Photo by Northfielder.

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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.

1. 1. Urban or rural?

2. 2. Urban or rural?

3. 3. Urban or rural?





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)

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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.

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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.


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.

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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.


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.

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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:

The world's population, concentrated

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.



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

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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.


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.

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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.

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


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.

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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.


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.


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

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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.


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

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