One number can't begin to capture the complexity of the differences between urban places—what we build, how we build it, what it looks like, and what it's going to take to maintain it.
But sometimes, one number can cut through all the details and illuminate a fundamental truth about some aspect of our world. It's why we measure statistics like the GDP or life expectancy: they don't tell us everything we need to know, but they do tell us a part of the story.
For example, take the answer to this simple question: Which countries have the most paved surface per capita?
Before I spoil it, think for a second about your gut reaction. What mental images do you associate with that question? Which do they look more like: A or B? Left or right?
It turns out we have data on that question. A widely cited study on impervious surface area per country was published in 2007 in the journal Sensors. The study defined impervious surface area (ISA) as including such things as “roads, parking lots, buildings, driveways, sidewalks and other manmade surfaces”—anything water will run off of instead of soaking in. The researchers devised a model that would estimate ISA by looking at the presence and brightness of nighttime lights in satellite imagery, along with population density. They tested the model on high-res aerial photos for accuracy, and then applied it worldwide.
The study found China, unsurprisingly, had the greatest total amount of ISA in the world, as the world’s largest country—but on a per capita basis, it wasn’t even close. A few representative results from the table are shown at right. (Click through to the study to see the rest.)
Which country had the most ISA per capita? The United Arab Emirates (home to Dubai and Abu Dhabi), followed by Canada, Finland*, and the United States.
Canada clocks in at 352.7 square meters per person of paved land. The US has 296.8 square meters.
(*If you have a guess on what Finland’s doing in this list, leave your theories in the comments. We’d love to hear them.)
So where was the photo on the right above taken? If you guessed Germany, you’d be correct. Germany’s ISA per capita is 103.1 square meters.
Germany has just over one-third of the paved surface per capita of the United States. We’re talking about two countries that are comparably wealthy, which are both famous for their freeways.
In fact, nearly all Western European countries have far less impervious surface per person than the United States, ranging from about 70% as much (Norway and Sweden) to well under half.
Even Japan, a wealthy country known for its dense “concrete jungle” cities, has only 114.5 square meters of paved surface per person, less than 40% of what the United States has. A typical suburban street in Japan looks like this:
Surprised? It’s understandable if you are. North American neighborhoods have a lot of greenery, while European and Japanese ones are not famed for it. Here’s the key to the dramatic difference the study reveals.
The Reason: Auto Orientation
There is a simple reason the US and Canada have so much pavement, and it has to do with why we have pavement in the first place. Impervious surfaces exist for three major reasons:
Streets and Roads
Two of those three have everything to do with cars. And on nearly every measure to do with car usage, well, America is number 1, baby.
Vehicle miles traveled per capita? Check. Number of cars owned per capita? Check. Low frequency of walking, biking, and public transit ridership? Check.
America’s post-WWII suburban experiment consisted of radically redesigning our cities around the automobile as not only a method of transportation, but the universal, all-but-obligatory method of transportation. Other countries around the world have adopted American-style suburban design to some extent, and have built freeways as well, but the US went all-in on this experiment like no other place. And Canada largely followed its lead.
We can be fooled by the fact that American-style suburbs are often visually verdant—plenty of trees, plenty of "green space." But in order to live in the development pattern our suburban experiment has produced, we are paving over far more of our land than Europeans in their compact, walkable cities are. (And, it should be noted, it’s not like Europeans don’t get to enjoy greenery at all in their cities: many have spectacular parks, such as Paris’s Bois de Boulogne.)
You can see the difference between urban and suburban areas within the United States as well. The US EPA maintains an EnviroAtlas with interesting data in an interactive map for a sampling of major metropolitan areas. Check out the striking pattern when you plot impervious surface per capita for a few major cities (click each map to view larger):
In every one of these cities, the lighter colors (less impervious surface) are in the traditional, pre-WWII neighborhoods, and the darkest colors are mostly in the suburbs (as well as some exceptions like industrial areas, or areas where very low population of any sort skews the numbers).
The paradox this data reveals is stark:
New York City is dominated by brick and glass and concrete and steel. But NYC residents have just about the least amount of pavement to their name of any Americans.
Why It Matters
Infrastructure is expensive. Most of the places we’ve built under the Suburban Experiment are choking on the costs of maintaining it, as we’ve documented again and again. And auto-oriented land uses are less financially productive, thus squeezing us at both ends.
Is the amount of paved surface per capita a perfect proxy for the dollar amount of infrastructure we’re committed to maintain? Not by a long shot—there are many complicating factors.
But, faced with the fact that the U.S. has vastly more pavement than many of its wealthy peer countries, and the fact that all those roads and parking lots will one day need repaving, should we be asking some tough questions? Absolutely.
Paving over land has environmental impacts. Flooding is a major concern in some of the most populous parts of the U.S., like the Eastern Seaboard (including New York), Florida and southeastern Texas. Environmental advocates in these places will often cite flood risk as a justification for mandatory "open space" policies that spread buildings farther apart from each other by requiring developers to leave a certain percentage of their property covered with vegetation which can absorb storm water. (In new suburban subdivisions, the required open space is often as high as 50%.)
In a particular area prone to flooding, of course, it's not paved surface per capita that really matters. It's the percent of all the land area that is paved—measured as impervious surface per square mile or per acre. That tells you how much of the rainwater that falls becomes runoff and needs to be accommodated somehow.
But is the solution to leave ample "green space" even in our walkable downtowns? Likely killing their financial productivity and their walkability in the process? Not at all.
Consider what Amsterdam looks like. The Netherlands has 123.2 square meters of impervious surface per capita, 40% of the U.S. total. The Netherlands is also largely near or even below sea level.
Rural areas of The Netherlands are perhaps less photographed, but their preservation is the flip side of the coin of the dense, walkable development pattern of Amsterdam, The Hague, etc. They’re quite green, and they can absorb a lot of water when it rains.
Let cities be cities, and rural be rural.
In productive places that generate wealth—the New Yorks, Amsterdams, Tokyos of the world—we can afford to deal with stormwater through more sophisticated technological means: pipes, pumps, levees, as well as newer technologies like green roofs and permeable pavement.
Places that produce comparatively lower revenue warrant a different approach, a more natural and low-tech one. It's not that verdant suburbs are always bad: it's that we should deal with drainage in those places by keeping our paved footprint to a minimum, and absorbing as much stormwater back into the ground as possible.
The lesson you uncover when you actually look at who builds the most pavement, and why, is that what appears green can be deceiving.
(Cover photos: Wikimedia Commons)