In Print: Planet of Cities

Planet of Cities sets an ambitious agenda—othing less than formulating evidence-based rules for managing the worldwide growth of cities during the 21st century. These rules attack the central ideal of the urban planner’s conventional wisdom—the Containment or Compact City Paradigm, showing it to be unworkable and unrealistic.

It must, the author argues, be replaced by the Making Room Paradigm, which rests on four propositions:

• Inevitable Expansion: City expansion cannot be contained; we must make room to accommodate it.
• Sustainable Densities: City densities must remain within a sustainable range, depending on the conditions; U.S. densities may be too low to sustain transit while densities in developing countries may be too high.
• Decent Housing: Strict containment of urban expansion destroys homes of the poor; urban land must be in ample supply to ensure decent housing for all.
• Public Works: As cities expand, land for streets, infrastructure, and open space must be secured in advance of development.

Shlomo Angel, a visiting fellow at the Lincoln Institute and a re­­searcher, consultant, and academic concerned with human settlements planning, found widespread reluctance around the world to confront the inevitable prospect of urban expansion. In response, he and his colleagues began to build a new "science of cities."

During the past decade, they created maps and analyzed satellite data, constructing metrics that enable them to test theories of urban growth.

Angel’s logic is simple: world urbanization is going to proceed apace, tapering off by the end of this century, and unless we act now to establish a framework of arterial roads and open space to guide this urbanization, the result will be an economic, fiscal, environmental, and social mess. However, the necessary action is blocked by the mythical goal of the contained city, expressed most forcefully in the U.S. smart growth literature, now being exported to Europe and the developing world.

Why would Angel say (some would make that how dare he say) that the contained city is a mythical goal? Isn’t there a consensus among urban planners and researchers that such cities are more sustainable, more accessible, and more environmentally friendly than their antithesis—urban sprawl? In fact, a recent planning journal article that mildly questioned the benefit of the compact city resulted in a furor of counter assertions.

Anticipating the controversy, Angel patiently refutes the contained-city argument with research evidence. First, he breaks down urban spatial structure into five dimensions: 1) urban land cover (urban extent or built-up area), 2) density, 3) centrality (proportion of the population living near the center), 4) fragmentation (scattered development), and 5) compactness (the degree to which the city footprint approximates a circle). Each of these is further broken down into detailed metrics to answer key questions and is carefully measured and analyzed.

Urban land cover analysis estimates that global urban land cover is expected to double in 20 years. However, it is still a very small per­­centage of land worldwide—less than one-half of 1 percent in 2000. Land is not in short supply, and containing growth is likened to holding back the tide.

Density analysis shows that urban densities have been declining almost everywhere for a century and will not slow down, contrary to many academics’ belief that densities are increasing. Even the notorious urban growth boundary of Portland, Oregon, has failed to increase the city’s density. The only question is how fast densities will continue to decline.

Centrality analysis shows that city form has gone from monocentric to polycentric, with workplaces distributed throughout the metropolitan area. This requires planning for mixed land use throughout the metropolitan fringe and for a networked grid of arterial roads and infrastructure.

Fragmentation analysis shows the global norm is that half of a city’s urban footprint is occupied by urbanized open space. As a rule of thumb, planned city expansion areas should be at least one-and-one-half times as large as the projected land requirements for the built-up area.

Compactness analysis shows that polycentric cities consume open space in order to maximize the accessibility of every location to every other location. To maintain a supply, open space must be reserved between the development corridors that follow radial transportation lines.

Expansion analysis shows that up to half of the area of projected urban growth will occur on cultivated land. In a worst-case scenario, some 6 percent of the land now under cultivation could be lost to urban expansion by 2050. Protecting the food supply will require both improved yields and expanding the amount of land under cultivation.

An actionable program for guiding urban expansion thus must be based on a Making Room Paradigm that includes realistic projections of urban land needs, generous metropolitan limits that do not pinch land supply, selective protection of open space, and advance reservation of rights-of-way for arterial road grids and infrastructure. In Angel’s view, anything less is a failure of imagination or nerve. He makes a strong case, especially for developing countries.