Researchers now can look across the growth trends in the world’s biggest cities over the course of a quarter century.
Basic rule of urban design: If you can see it on a map, you’ve got a better chance of being able to lay out a thoughtful plan for development.
That’s the impetus behind the recent upgrade to the Atlas of Urban Expansion, a project of the Lincoln Institute of Land Policy, UN-Habitat and New York University. First released in 2012, the atlas gives extensive data about the growth of 200 cities, selected to be a representative sampling of the 4,231 cities and metropolitan areas worldwide that had populations of 100,000 or more in 2010.
The updated atlas incorporates data from 2014 and 2015 into the original data set, which included statistics culled between 1990 and 2000. Researchers now can look across the growth trends in the world’s biggest cities over the course of a quarter century.
Data on urban sprawl will be crucial as human beings attempt to accommodate one another on an increasingly crowded globe.
“In 2050, we are expecting another two and a half billion people to be living in cities across the planet. The vast majority will be in cities in developing countries, and understanding their characteristics of development is incredibly important to the quality of life and to the health of the planet," said Armando Carbonell, senior fellow and chair of the Department of Planning and Urban Form at the Lincoln Institute of Land Policy. "How they are housed and how they get around will impact climate change and a range of other factors.”
The newly added data discloses a number of interesting trends.
In the developed world, cities continue to expand their footprint, but the rate of increase is slowing. Just as birth rates tend to slow as nations become more affluent, “we see a similar tendency with land consumption per person,” Carbonell said. “It’s not coming down yet, but it is going up more slowly. If this continues, we may come to the point where we max out the sprawl factor.”
The same cannot be said in the developing world, where the newly updated atlas shows the urban land grab rolling ahead at a thunderous clip. While the population in these areas has doubled in the intervening years, land consumption around urban areas has rocketed up three and a half times.
There are different ways to view such information. On the one hand, the urban expansion suggests greater material well-being. “Poor people tend to occupy very little space, and now the norm appears to be that people are occupying a lot more space. So this is not necessarily a bad thing per se. It means that people are probably a little better off than in the past,” Carbonell said.
But there is potential risk associated with rapid urban sprawl, especially in the developing world. “Most of this development is unplanned, informal, not part of the regulated system," he said. "There is a lot of relatively haphazard development, which means it does not necessarily provide for things like arterial roads that make bus service possible. It doesn’t allow for open space or recreational opportunities,” he said.
This in turn can have negative environmental consequences. Poorly organized traffic, for instance, tends to generate more greenhouse gases.
The updated atlas arrives amid a global call for nations to pay closer attention to the ways in which their cities grow.
“By 2030, urban areas are projected to house 60 per cent of people globally and one in every three people will live in cities with at least half a million inhabitants,” notes the United Nations publication The World’s Cities in 2016. “Understanding the key trends in urbanization likely to unfold over the coming years is crucial to the implementation of [sustainability goals] and for efforts to forge a new framework of urban development” under international consensus.
Sustainability is a common theme among those concerned with the pace of urbanization. Take for instance the simple matter of trees. Researchers at the University of Iowa say the density of potentially toxic particulate matter near a tree drops by 7 to 24 percent. Having an atlas that shows the availability of open areas could help planners to appropriate more green space.
The atlas aims to make just such connections. Some of the data included in the map charts the density of urban areas, as well as fragmentation, the degree to which cities expand in discontinuous leaps.
Other metrics look at infill, new density added to existing urbanized open space since the last map was issued, as well as leapfrogging, new urban clusters that are not attached to the urban extent of the earlier period.
The atlas offers data on urban extent density, the ratio of the total population of the city and its urban extent, measured in persons per hectare. Here the difference between the developed and developing worlds becomes clear. Los Angeles for instance became slightly more dense from 1990 to 2014, going to 25 to 26 persons per hectacre. Addis Ababa by comparison has sprawled, with density dropping from 125 to 102 persons per hectacre between 1986 and 2010.
The metrics may seem arcane to the layman, but they are bread and butter to researchers trying to make sense of the explosive and often chaotic growth within the urban environment.
To help put these numbers into context, the authors of the atlas have created historical animations that show dramatically just how fast and how far 30 cities have spread over the time period covered by the data.
Much of that growth has occurred in China and Africa, while in the developed world the pace of expansion is slowing. Other researchers have noted this effect as well.
In a recent publication, the Congress for the New Urbanism notes that while the top 25 “sprawling cities” in the United States are still growing at a brisk clip, they growth now shows less fragmentation, less of a tendency toward sprawl.
Growth today encompasses neighborhoods: It’s more coherent than in the past. “Because of their era of rapid growth, sprawling cities experienced maximum fragmentation of the built environment. Now these cities have rediscovered the value of building cohesive neighborhoods and centers,” the authors note.