New research in a book published by the Lincoln Institute of Land Policy, Planet of Cities suggests that most cities of the world are woefully unprepared for the urban population explosion that will occur through the 21st century.
Planners and political leaders must begin acting now to establish basic infrastructure and make realistic projections for needed urban land, while at the same time setting aside critical green and open space, says author Shlomo "Solly" Angel, a visiting fellow at the Lincoln Institute.
The book was announced at the World Urban Forum VI in Naples. Angel presented the book's main findings at the opening dialogue there and also discussed his companion volume, Atlas of Urban Expansion, published earlier this summer.
In 2010 more than half of the world's total population lived in cities – a share expected to increase to 70 percent or more by 2050. This means the world's urban population is projected to grow from 3.5 billion in 2010 to 6.2 billion in 2050. Almost all of these new urban residents will be in developing countries.
Although concern about sprawl in the United States, and to a certain extent recently in China, has focused on smart growth, containment, urban growth boundaries, compactness, and density, that approach is not appropriate for cities in developing countries where population densities are four times greater than in U.S. cities. Those areas are likely to more than triple their developed land areas by 2050.
Planet of Cities instead suggests a "making room" paradigm to come to terms with the expected expansion of cities, particularly in the rapidly urbanizing countries in Asia and Africa, and to make the minimally necessary preparations.
The paradigm is predicated on four propositions:
The expansion of cities due to urban population growth cannot be contained. Instead we must make adequate room to accommodate it.
City densities must remain within a sustainable range. If density is too low, it must be allowed to increase, and if it is too high, it must be allowed to decline.
Strict containment of urban expansion destroys the homes of the poor and puts new housing out of reach for most people. Decent housing for all can be ensured only if urban land is in ample supply.
As cities expand, the necessary land for public streets, public infrastructure networks, and public open spaces must be secured in advance of development.
Planet of Cities and Atlas of Urban Expansion are the culmination of a decade of research by Angel and his team. They make an important contribution to a new science of cities for the 21st century.
"Nearly 4,000 cities on our planet today have populations of 100,000 people or more. We know their names, locations, and approximate populations from maps and other data sources, but until now there has been little comparable knowledge about them, and none that could be described as rigorously scientific," Angel says. "We need a science of cities based on studying all these cities together—not in the abstract, but with a view to preparing them for their coming expansion."
The first part of Planet of Cities explores the planet's urbanization from an historical and geographical viewpoint, to establish a global perspective for the study of cities. It documents the breathtaking urbanization that began in the 19th century, has accelerated so that half the world population now resides in urban areas, and will come to a close, possibly by the end of this century, when most people who want to live in cities will have moved there.
The second part of the book seeks to "lessen our fear of urban expansion," Angel says, by examining key attributes such as the current extent of urban areas and their speed of expansion; current population densities and their changes over time; the way residences and workplaces in cities are centralized or disperse to the periphery over time; and the extent of fragmentation in built-up areas of cities and how levels of fragmentation change over time.
Planet of Cities also explores the shapes of urban footprints and how their levels of compactness change over time, how much land urban areas will require in future decades, and how much cultivated land will be consumed by expanding urban areas.
By answering these questions and exploring their implications for action, Planet of Cities provides the conceptual framework, empirical evidence, and practical agenda necessary for the minimal yet meaningful management of urban expansion.
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