Urban Expansion: Better Data, Realistic Planning

+ Brandon Fuller

This week’s edition of The Economist discusses the growing availability of urban data, data that can inform more realistic planning efforts and improved city management. The article highlights the work of Solly Angel, a scholar here at the NYU Stern Urbanization Project:

Shlomo [Solly] Angel, an urban planning expert at New York University, gathered historical and census data from hundreds of cities, digitised thousands of maps and had computers count millions of pixels on satellite pictures. Between 1990 and 2000 the surfaces of each of the 120 cities he and his team studied grew on average more than twice as fast as their populations. These rates, he says, are unlikely to change. That means that the amount of urban land will double in only 19 years, whereas the urban population will double in 43 years.

City densities in the developing world are often far higher than densities in the developed world and well in excess of the density neeeded to support public transportation. Even if cities in the developing world maintain current densities, rural-to-urban migration will cause the cities to grow outward. Should incomes in the developing world continue to rise relative to transportation costs, densities will very likely decline further as families demand more living space. Solly therefore encourages politicians and planners in the developing world to come to terms with urban expansion.

Instead of trying to limit growth, planners should “make room”, says Mr Angel: be realistic when projecting urban land needs, set generous metropolitan limits, protect some open space and provide an arterial grid of roads. This is pretty much what New York did in the early 18th century.

For Solly, trying to contain urban expansion in the developing world is like trying to hold back the tide — you’re only going to get your feet wet. A strategic plan for accommodating urban expansion can better capture economic and environmental benefits — keeping housing affordable and ensuring that people can easily walk to public transportation on an appropriately spaced grid of arterial roads.

The notion of accommodating urban expansion may seem at odds with the environmental tenets of pro-density advocates in places like the United States, but the context in the developing world is very different. In “Making Room for a Planet of Cities,” Solly notes that declining densities in the developing world needn’t mean car dependent commuting patterns:

The average built-up area density in cities in developing counties in 2000 was 129 p/ha. Even if it declined at 2 percent per annum, the most pessimistic scenario, it will still be 47 p/ha in 2050, more than double the average built-up area density in U.S. cities in 2000 (21 p/ha), and—given expected lower levels of car ownership—high enough to sustain both public transport and informal transit services.

If policymakers select a strategy of containment (or no strategy at all), the tide of urban expansion is unlikely to stay out — it will advance at a similar pace, albeit informally. Without coordination of an arterial road network, informal settlement in rapidly growing cities will likely result in the kinds of congestion and public transportation constraints seen in cities like Bangkok. The kind of congestion that unnecessarily reduces economic access for lower-income families.

In a forthcoming book, Solly will delve deeper into the data to tackle these and other urban policy issues. More as the publication date nears.

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