CityReads│Mapping Urban Expansion: Past, Present and Future

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Mapping Urban Expansion: Past, Present and Future

The Atlas of Urban Expansion—2016 Edition focuses on the land converted to urban use in the past 25 years in a global representative sample of 200 cities. 

Angel et al., Atlas of Urban Expansion—2016 Edition, Volume 1: Areas and Densities, New York: New York University, Nairobi: UN-Habitat, and Cambridge, MA: Lincoln Institute of Land Policy, 2016.

Sources: http://www.lincolninst.edu/publications/other/atlas-urban-expansion-2016-edition

http://www.atlasofurbanexpansion.org/

In the books, Planet of Cities together with its companion volume, Atlas of Urban Expansion, published in 2012, Shlomo Angel puts into question the main tenets of the familiar Containment Paradigm and proposes an alternative Making Room Paradigm that seeks to come to terms with the expected expansion of cities instead of seeking to contain it (To learn more, please refer to From"Containment Paradigm" to "Making Room Paradigm”). 

In 2016, Shlomo Angel and his research teams from the Lincoln Institute of Land Policy, UN-Habitat, and New York University, put together a two-volume 2016 edition of Atlas of Urban Expansion. Volume I covers areas and densities. Volume II covers blocks and roads.

The 2016 edition focuses on a carefully chosen sample of 200 cities from the entire universe of cities—all 4,231cities and metropolitan areas that had 100,000 people on more in 2010. It illustrates how 200 of the world’s fastest growing cities have expanded physically from 1990 to 2015, which can inform us about the universe of cities as a whole. Based on the online Atlas of Urban Expansion, an open-source database of satellite imagery, coupled with population figures and other data, these volumes characterize the quantity and quality of urban growth in additional detail.

The 2010 Universe of Cities, comprising a total of 4,231 cities that had 100,000 people or more in 2010.

The Atlas of Urban Expansion—The 2016 Edition provides maps and estimates of the dimensions and attributes of urban expansion in a global sample of 200 cities. These maps and estimates should help us examine two sets of simple questions. First, what are the physical extents of urban areas on our planet today, what are their key attributes, and how and why are they changing over time? Second, how well configured are recently built urban peripheries, and how and why are layouts changing over time?

The sample shows land consumption increasing at an unsustainable rate, tripling as populations double. Urban expansion, particularly at the periphery of sprawling metropolitan areas, especially in the developing world, lacks open space, short blocks for walkability, and access to arterial roads to help people get to work, and thus degrades quality of life, economic development, and the environment.

Humanity is in the midst of its most ambitious project, the Urbanization Project. This project, which entails accommodating increasing numbers of people in cities, started in earnest at the beginning of the eighteenth century when less than 10% of the people lived in cities, and will be largely complete by the end of the twenty-first century when three-quarters or more of humanity will live in cities. By 1950, only 30% of the world’s population resided in cities. That share increased to 54% by 2015 and is now expected to increase to 66% by 2050. The world’s urban population is expected to increase from 4.0 billion in 2015 to 6.3 billion in 2050, and almost all of this growth is expected to take place in less developed countries. Cities in more developed countries will add only 130 million people to their populations during this period. Cities in less developed countries will need to absorb 18 times that number, or close to 2.3 billion people, thereby increasing their total urban population of 3.0 billion in 2015 by 75%.

The population of cities in less developed countries doubled between 1990 and 2015, for example—the time period covered in this Atlas—and their urban extents increased on average by a factor of 3.5. In parallel, the population of cities in more developed countries increased by a factor of 1.2 between 1990 and 2015; their urban extents increased by a factor of 1.8.

The areas of cities are growing at a faster rate than their populations, in part because economic development results in more consumption in general and more land consumption per capita. In fact, average urban densities in less developed countries—3.3 times higher than densities in more developed countries in 1990—declined at an average annual rate of 2.1% between 1990 and 2015. In more developed countries, densities declined at 1.5% during this period. 

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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.

By now, it should be clear that we cannot hope to slow down the urbanization process or to shift populations among cities. People are free to move within their own countries and their right to move is enshrined in the Universal Declaration of Human Rights. We know that population growth in cities large and small cannot be guided by policy effectively. But the conversion of land from rural to urban use is very much guided and influenced by policy.

An initial inspection of urban layouts in the global sample of cities suggests that most of the residential fabric in the expansion areas of cities (1990–2014), especially in less developed countries, is unplanned and disorderly, taking place in defiance of municipal plans or regulations. It suggests that the share of urban lands that are laid out before occupation is declining over time; it also suggests that the share of the areas of cities within walking distance of arterial roads is declining as well, failing to connect urban peripheries effectively to metropolitan labor markets, making cities less productive, less inclusive, and less sustainable. The share of the land allocated to streets in newly urbanized areas is also declining. Substantial areas on the urban fringe consist of large city blocks and a very small share of intersections that are 4-way, which creates traffic jams and compromises walking and biking. In addition, the average block size is increasing over time.

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. To meet this goal, cities need concerted public action—action that secures adequate lands for public works and public open spaces in advance of development, for example—that precedes and guides the operation of the free market on the urban fringe. In the absence of concerted public action, land and housing markets, efficient as they may be in theory, will fail to perform properly in practice.

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