Shutterstock

Why do some cities – and neighborhoods – have so much more "urban nature" than others?

The physicist Geoffrey West and his collaborators famously found that cities obey some universal scaling laws in the same way that much of biology does. Take the population of a city anywhere in the world, and these laws can predict with startling accuracy the size of the city’s road network or its output in patents or its quantity of crime. This is because so much about urban life scales to population. The larger a city gets, the less infrastructure it needs per capita. At the same time, as populations increase, problems like crime and benefits like intellectual property proliferate at an even greater rate than one-to-one (when a city doubles in size, for instance, it produces more than twice the patents).

In these reliable, mathematical ways, cities mimic nature. And yet, ironically, there is one element of cities that doesn’t seem to follow any scaling law: nature itself.

Nature – and it’s an admittedly slippery term that you can define multiple ways – is spread within and across cities with wild variability. Some small cities have lots of public parks, or lots of greenery as seen from satellites, while some larger cities have notably less of it. There’s no neat relationship between city population and parks per capita, or tree cover or even space that’s simply unpaved.

"Whenever you see that great variation in data, it begs for analysis and possible explanation," says Jon Christensen, an adjunct assistant professor in the history department at UCLA.

He and collaborators at Stanford began studying the question using a large set of updated data from the Trust for Public Land’s ParkScore project, which looked at park metrics in America’s 40 largest cities. Christensen and Stanford digital humanities research developer Karl Grossner are presenting some of the findings this week at the annual meeting of the American Association of Geographers. More relevant for the rest of us, they’ve also created an intricate, interactive public exploration of the question online.

2,661 "naturehoods" mapped on City Nature

The project, City Nature, offers comparisons of urban nature across cities, as well as an analysis of 2,661 "naturehoods," or neighborhoods within 34 cities where you can contrast the presence of greenery against home values, population density, and racial diversity. The project also contains a textual analysis of planning documents for mention of nature and greenery.

Why, though, does the question of scale matter? In his book The Triumph of Cities, Edward Glaeser argued that the conservation and preservation of open space in cities gets in the way of their economic growth (among other things, driving up the cost of scarce housing in places like San Francisco). Some of Christensen’s earlier research in Silicon Valley suggested this wasn’t true. “I thought,” Christensen says, “there’s something not quite right about this theory of the city, of nature being an impediment to the efficient economic development of cities for people.”

But if there’s no clear relationship between the presence of nature in cities and their population, it’s hard to make the argument that nature impedes development. To illustrate this, using City Nature’s tools, this is a chart of park area in 38 large American cities compared to population:

That big teal circle at far right is New York City (the dots are colored by geographic region and sized by population). The little lime-green outlier up top is Jacksonville. Chicago, a city with a seemingly deep history of park planning dating to Daniel Burnham, is that large blue circle with more than 2 million people but less than 20,000 acres of park area.

Here is a comparison of ParkScores from the Trust for Public Land with the land area (in square miles) of cities:

Christensen and Grossner have tried to come at the question from multiple angles, assessing numerous variables (weather, geographic region, even the historic influence of the Olmsted Brothers landscape design firm) and multiple measures of nature ("greenness" and "unpavedness" in addition to the presence of parks).

"There doesn’t seem to be any one factor that can explain that variation," Christensen says. Park area and total land area correlate somewhat, although it isn't surprising that as cities would grow in physical size, so, too would the physical mass of parkland.

Patterns similarly disappear in comparing the presence of nature with home values or home-ownership down to the neighborhood scale. "There’s weak correlation at best between any of these social variables," Grossner says, "and the degree of greenness and/or ‘pavedness’ and/or park need, and/or percent park."

All of this essentially means that while no hard rules or correlations govern the presence of nature in cities, historians have to look instead for the very specific ways that individual communities prioritized and planned for its inclusion throughout history. And this is a much bigger task than the 40-city statistical analysis.

"That’s the way in which this broadly comparative project also becomes a historical project to try to understand what it is that explains this variation," Christensen says. "What are the choices that have been made in different cities, and how has that shaped cities?"

Top image: 06photo/Shutterstock

About the Author

Most Popular

  1. Construction workers build affordable housing units.
    Equity

    Why Is 'Affordable' Housing So Expensive to Build?

    As costs keep rising, it’s becoming harder and harder for governments to subsidize projects like they’ve done in the past.

  2. Equity

    The Side Pittsburgh Doesn't Want You to See

    Pittsburgh filmmaker Chris Ivey has spent over twelve years documenting the lives of the people displaced so that the city can achieve its “cool” status.  

  3. Transportation

    If You Drive Less Than 10,000 Miles a Year, You Probably Shouldn't Own a Car

    Up to one-quarter of all U.S. drivers might be better off using ride-sharing services instead.

  4. Transportation

    How Seattle Bucked a National Trend and Got More People to Ride the Bus

    Three experts in three very different positions weigh in on their city’s ridership success.

  5. People use leaning bars at a bus stop in Brooklyn in 2016.
    Design

    Cities Take Both Sides in the 'War on Sitting'

    Cities are removing benches in an effort to counter vagrancy and crime—at the same time that they’re adding them to make the public realm more age-friendly.