All posts by Tim De Chant

The purported rise of the sharing economy

Gabriel Metcalf and Jennifer Warburg, writing in The Urbanist:

Under the name “collaborative consumption,” or sometimes simply “the sharing economy,” a new type of enterprise is emerging that strives to make it easy for people who don’t know each other to share resources. Habits of sharing that have existed within small, informal networks for most of human existence (say, borrowing your neighbor’s lawnmower or letting a friend crash on your couch) have now blossomed into a market for micro-entrepreneurship that spans the globe.

I think the press surrounding the sharing economy is bigger than its actual impact. We trumpet car sharing as a canonical example, but it’s an experiment that’s just over a decade old. Yes, it’s successful, but people who own cars still greatly outstrip people who rent. I don’t think we have enough data to call the sharing economy a definitive trend, let alone nail the lid on the coffin of ownership. 

Furthermore, I’m not convinced renting is going to replace owning in any significant way. As humans, we like collecting—just ask anyone who has shelves loaded with movies, books, or records. Renting is the antithesis of that. 

The geography and spatial allocation of greenhouse gas emissions

Brendon Slotterback:

A finer grain of detail will help target local emissions-reduction strategies.  However, as our emissions measurement tools get better, we need to make sure not to miss the key land use-transportation connection that drives a big portion of greenhouse gas emissions.

Allergies and urban biodiversity

Rob Dunn, writing for Conservation Magazine:

The parallels in geography and timing between urbanization, the loss of biodiversity, and the rise in immune-system problems raise an intriguing—and troubling—question. Could our distance from nature and our chronic immunological discontent be related? Some now say . . . yes.

Keys to the City

Literally. Geoff Manaugh: 

A set of “master keys” to the infrastructure of New York City popped up on eBay last month, leaving many public commentators and city officials alike concerned for the safety of the metropolis.

Security implications aside, some of these keys are delightfully archaic.

Live on KCBS

I’ll be talking live today at 9:20 AM Pacific time (12:20 Eastern) with KCBS about the economic impact of Sudden Oak Death in the San Francisco Bay Area. It’s a topic that I care deeply about—my dissertation work focused on coast live oaks, one of the trees that’s been decimated by the pathogen. Hit the link above to listen in.

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.


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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Republicans to Cities: Drop Dead

The headline writers win this round. But once you get past the incendiary headline, author Kevin Baker presents a solid case that the Republican Party really wants nothing to do with urban areas. I think that stems partly from the fact that, as a conservative party, they want America to be the land it once was—a nation of farmers, or in its modern translation, a nation of small businessmen tending their suburban acreage. But reality is a harsh mistress, and the GOP will have to change eventually to woo the increasingly urban masses. 

How to grow living walls

Green façades are a bit of a trend in architecture these days, but actually growing plants on a vertical surface is a real challenge. This case study examines the process in great detail.

Demographics of Middle Earth

Here’s a fun one. Emil Johansson compiled a complete statistical analysis of the various populations in J.R.R. Tolkien’s The Hobbit and Lord of the Rings series. 

The Next Pandemic: Why It Will Come from Wildlife It Will Come from Wildlife

David Quammen, writing for Yale e360:

Experts I’ve interviewed over the past six years generally agree that such a Next Big One is not only possible but probable. They agree that it will almost certainly be a zoonotic disease — one that emerges from wildlife — and that the causal agent will most likely be a virus. They agree that sheer human abundance, density, and interconnectedness make us highly vulnerable. Our population now stands above seven billion, after all, a vast multitude of potential victims, many of us living at close quarters in big cities, traveling quickly and often from place to place, sharing infections with one another; and there are dangerous new viruses lately emerging against which we haven’t been immunized. Another major pandemic seems as logically inevitable as the prospect that a very dry, very thick forest will eventually burn.

I’m sure this is just a taste of what Quammen has in store in his new book, Spillover. I just got mine in the mail and can’t wait to sink my teeth into it.

New Yorkers, It’s Tree Planting Season

PSA for New York readers:

The Bloomberg administration’s initiative to plant one million new trees in New York City is past the halfway mark but still has a long way to go. To broaden a canopy that beautifies the city while also filtering pollution and reducing stormwater runoff, the New York Restoration Project has scheduled tree giveaways in all five boroughs in October and November.

My how times change

Freeways and parking, 1948

Eric Fischer:

From Traffic Engineering, July, 1948.

Presumably the parking lot is intended to represent people successfully reaching their destination, not blighting of the landscape, but it’s hard to read it that way now.

Why Your Car Isn’t Electric

Maggie Koerth-Baker:

Society shapes the development and use of technology (this is a function of social determinism; for example, cars didn’t really become ubiquitous until they became easy to operate and cheap to buy), but technology also shapes society (technological determinism; think of the way cars then essentially created the suburbs). Over time, the two interact with and change each other, an idea known as technological momentum, which was introduced in 1969 by Thomas P. Hughes, a historian of technology. According to Hughes’s theory, the technologies we end up using aren’t determined by any objective measure of quality. In fact, the tools we choose are often deeply flawed. They just happened to meet our particular social needs at a particular time and then became embedded in our culture.

Unintended side effects of white roofs

Umair Irfan, reporting for ClimateWire:

Cool roofs — created when developers use reflective paint on rooftops — do perform their intended task of reducing temperatures in urban areas while cutting building energy costs. However, they shift rainfall patterns by reducing evapotranspiration, the process by which water evaporates from the ground and enters the atmosphere. In the maximum expansion scenario, cool roofs led to a 4 percent decline in rainfall.

Romney’s $90 billion green jobs attack

Juliet Eilperin and Steven Mufson, writing for the Washington Post, deconstruct Romney’s green energy claims from Wednesday’s debate:

The Energy Department put $90 billion worth of grants, loan guarantees and loans into what it calls a “clean energy” economy. But that money is spread widely: About $3 billion went to carbon capture and storage projects needed to make coal “clean,” a goal Romney shares; about $11 billion went to energy efficiency; about $5 billion went to clean up old nuclear weapons sites; about $4 billion went to modernizing the electricity grid; and about $2 billion went to research and development, which Romney has also supported.

S.F. port plan shifted to allow for rising sea

John King:

While skeptics do their best to ignore our ever-more-tumultuous weather patterns, planners in coastal settings already are coping with the sea level rise that might result from climate change.

The Golden Gate at 75

The Golden Gate Bridge turned 75 years old this year. I was in the Bay Area during the diamond jubilee, and though I wasn’t able to attend any official event, I did cross the span twice. It’s a marvel. Jon Christensen interviewed John King, the San Francisco Chronicle’s urban design critic, and Anthea Hartig, the California Historical Society’s executive director, on the bridge’s historical and cultural importance a few months back, just before the celebration.

The Forgotten Mapmaker

Alexis Madrigal, with part two in his series on web mapping:


As I described last month, Google has spent literally tens of thousands of person-hours creating its maps. I argued that no other company could beat Google at this game, which turned out to be my most controversial assertion. People pointed out that while Google’s driven 5 million miles in Street View cars, UPS drives 3.3 billion miles a year. Whoever had access to these other datasets might be in the mapping (cough) driver’s seat.

Well, it turns out that Nokia is the company that receives the GPS data from both FedEx and UPS, the company’s senior VP of Location Content, Cliff Fox, told me.

Those datasets are a real goldmine. Wonder how Nokia (or Navteq, back when they were independent) swung that?


Planet of the cities

Endless city

Science fiction is littered with planet-wide cities. Star Wars had Coruscant, Isaac Asimov’s Foundation Series had Trantor, and even Star Trek, in an alternate timeline in First Contact, saw Earth paved over by the cybernetic Borg. City-planets are both a wonder and a terror—we stand in awe of our power to change the world, but also regard that ability with fear. What if we actually did it? Hundreds of years ago, it didn’t even seem possible. But the quickening pace of population growth in the 1800s changed that, and the vast environmental changes sweeping the planet today are a stern reminder of just how powerful we are.

Of course, Earth is not in any immediate danger of becoming one conurbation, but the trend isn’t promising. Urban areas around the world are expanding at double the rate of their populations. That means every person who moves to or is born in a city will, on average, take up more space than the person before them.

And soon there will be a lot more people wanting that extra space. Urban populations are expected to swell to 5 billion in the next two decades, and according to a recent study published in the Proceedings of the National Academy of Science, cities are expected to gobble up another 460,000-plus square miles (1.2 million square kilometers). Put simply, it means that cities will occupy three times more land in 2030 than they did in 2000.

That’s a staggering amount. The results are equally astounding. The east coast of China is likely to merge into one massive city. Cities in the region spanning Lake Victoria’s north shore—an arc from Burundi to Kenya—will swell 1,900 percent in area. Urban areas along the coastal strip from Côte d’Ivoire to Nigeria will grow 920 percent. Other countries like India, Mexico, and Turkey will also experience outsize urban growth. Even developed regions like North America and Japan will have to endure massive urban expansion.

There’s a lot to be concerned about with these statistics. Urban areas that grow several-fold in a few decades won’t be happy places to live—they’ll likely be dominated by slums, or at the very least snarled with traffic and choked with pollution. The situation is even more dire for the ecosystems they’ll be displacing, which are some of the most diverse in the world. That’s because we humans prefer to live in dangerous places, places dominated by disturbances like earthquakes, volcanoes, tsunamis, and floods, processes that produce rich and diverse ecosystems. As a result, the next two decades of urban expansion will imperil nearly 140 amphibian species, more than 40 mammal species, and 25 bird species.

That doesn’t mean we should halt progress and send everyone back to the farm. Cities are still more environmentally friendly on a global scale than the alternative. No, what it means is that we need to think hard—and fast—about how we’re going to cope with the booming urban areas of the next two decades. Much of that growth is going to happen in places like Africa that haven’t had large cities historically. Nigeria, for example, is projected to have more than 400 million people in 2050. That’s more that double its present population.

Success will depend on thinking big. It’ll require “more holistic policies that integrate traditional urban sectors—transport, energy, sanitation, buildings—with land use and conservation,” the study’s authors write. A “science of the city” that others have been arguing for. Developing that science is, in my mind, the only hope we have of taming these urban beasts. The cities of the future may not be the planet-consuming behemoths of our techno-futuristic tall tales, but they’ll be beyond anything we’ve ever seen before. We’ll need a science that’s equally formidable.


Seto, K.C., Guneralp, B. & Hutyra, L.R. (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools, Proceedings of the National Academy of Sciences, 109 (40) 16088. DOI: 10.1073/pnas.1211658109

Photo by Carl Lovén.

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