New York University Professor Shlomo Angel and his colleagues (Alejandro M. Blei, Jason Parent, Patrick Lamson-Hall, and Nicolás Galarza Sánchez, with Daniel L. Civco, Rachel Qian Lei, and Kevin Thom) have produced the Atlas of Urban Expansion: 2016 edition, which represents the most detailed available spatial analysis of world urbanization, relying on a sample of 200 urban areas. It was published jointly United Nations Habitat, New York University, and the Lincoln Institute of Land Policy and released in conjunction with the Habitat III conference in Quito. The Atlasfollows the publication of Angel's Planet of Cities, published by the Lincoln Institute of Land Policy which was reviewed in New Geography in A Planet of People: Angel's Planet of Cities.
In his Foreword, Joan Clos, Under-Secretary-General, United Nations and UN-Habitat Executive Director Joan Clos describes the Atlas findings as "quite shocking." Indeed, for urban planners and others who have been misled into believing that the cities of the world are becoming denser as they grow larger, the message of the Atlas should be a "wake-up call."
In his Foreword, Professor Angel notes that: "The anti-sprawl agenda—decrying unplanned, low density, fragmented and non-compact urban expansion—has been guiding city planners for decades and we now find that the majority of cities have adopted land use plans that seek to contain their outward expansion in one form or another." The clear message is an inconvenient truth that despite such planning, urban areas have continued to expand spatially faster than they had added population. Worldwide urban densities continue to drop virtually without regard their relative affluence or poverty.
Under-Secretary-General Clos describes the purpose of the Atlas as: "to provide informed analyses to policy makers, public officials, research administrators, and scientists for use in their decision-making processes. In this sense, the Atlas of Urban Expansion is part of the emerging ‘science of policy’ that is dedicated to the production of knowledge that best serves the public interest." Obviously, that is a laudable goal and improving cities --- which at a minimum requires both improving affluence and reducing poverty --- should design their policies to achieve these objectives.
The Atlas shows that the densities of urban areas have been dropping 1.5 percent annually over the past 25 years in more developed countries. The decline in density has been even greater, 2.1 percent, in less developed countries, which is where the vast majority of urban growth is taking place. The Atlas predicts that this trend will generally continue.
These trends are likely to continue in one form or another. Between 2015 and 2050, urban extents in more developed countries can be expected to increase by a factor of 1.9 at the current rate of increase in land consumption, by a factor of 1.5 at half the current rate, and by a factor of 1.1 if land consumption per capita remains constant over time. During this period, urban extents in less developed countries will increase by a factor of 3.7 at the current rate of increase in land consumption, by a factor of 2.5 at half the current rate, and by a factor of 1.8 if land consumption remains constant.
The Atlas has data that will not be found anywhere else, as it delves deep into the fabric of the urban area sample. There is data for each of the urban areas on each of these measures (too detailed for examination here): fragmentation, compactness, infill development and "leap frog" development.
Some of the individual urban area density trends over the past 25 years are particularly shocking. For example:
• Guangzhou, China (which includes the urbanization of huge Foshan) is now 10 times its 1990 population, yet has experienced an urban density decline of about 75 percent.
• Seoul has added more than a third to its population, yet its urban density has dropped by more than 50 percent.
• Bangkok's urban population density dropped by one-third, even as the population more than doubled.
• Budapest and Warsaw have seen their urban densities decline by more than 40 percent.
• Tokyo, Paris, Tehran, and New York have experienced urban density reductions of at least 20 percent.
• Mumbai, still the fourth highest urban density in the sample, has dropped more than 10 percent, as have Santiago, Chile and Buenos Aires. Since the 1947 census, virtually all population growth in Buenos Aires has been suburban (outside the core city of Buenos Aires).
• Curitiba, Brazil, which has received at least as much international acclaim from urban planners for its model policies as Portland, has seen its population density drop one third in the last 25 years. Still, Curitiba's urban density is nearly triple that of sprawling Portland (which ranks 189 the out of 200 in urban density, see Note 1).
One of the exceptions to the falling density "rule of thumb" is Dhaka, which the Atlas shows as having the highest density of any urban area (Note 2). Dhaka's urban density has risen three percent over the last 25 years, as much of the additional population has been housed in low-rise, unhealthful shantytowns (see: The Evolving Urban Form: Dhaka), where densities are reported to be as high as 2.5 million per square mile or 1 million per square kilometer (photograph above). This is 35 times the 70,000 per square mile density of Manhattan (27,000 per square kilometer) in 2010.
As the Atlas puts it: "When cities grow in population and wealth they expand. As cities expand, they need to convert and prepare lands for urban use. Stated as a broad policy goal, cities need adequate lands to accommodate their growing populations and these lands need to be affordable, properly serviced, and accessible to jobs to be of optimum use to their inhabitants." The concern of the Atlas is that this urban expansion be well managed.
As The Economist has pointed out, suburbanization (pejoratively called urban sprawl) can be stopped only forcibly, "But the consequences of doing that are severe." Urban residents can only hope for a future of policies fashioned from reality rather than dogma.
Note 1: Portland's urban density lower than that of 94 of the 200 urban areas in the Atlas sample. This is nearly the same as its the ranking in Demographia World Urban Areas, where Portland's urban density is lower than that of 93 percent out of more than 1000. Demographia World Urban Areas provides population, urban land area and urban population density for the more than 1000 identified with 500,000 or more population.
Note 2: Dhaka is also shown to be the highest density urban area in Demographia World Urban Areas, which provides population, urban land area and urban population density for the more than 1000 identified with 500,000 or more population.