As cities spread into surrounding territories, roadways clog, pollution increases, social inequities expand, and the costs of municipal services like sewers and the police rise. Or do they? University of Toronto economist Matthew Turner and his colleagues decided to quantify one component of change: urban sprawl. They compared satellite images of the entire continental United States in 1976 and 1992, the most recent year complete data were available, and divided the country into 8.7 billion 98-foot squares to examine the question in unprecedented detail.
Predictably, the photo evidence revealed that America has grown: Nearly 2 percent of the country was paved by 1992, for example, a third more than in 1976. Not so predictably, the percentage of growth that is sprawl is not increasing. "Although there is more development, on average, that development isn't any more scattered," Turner says. In other words, modern American cities are really just bigger versions of older American cities.
Turner's observations of individual cities are also surprising. Miami, for example, is about a third more compact than either New York or San Francisco, while Pittsburgh sprawls more than even Atlanta or Washington. He attributes about 25 percent of the difference to topographical factors like groundwater accessibility, weather, and mountains. The rest is pure human influence: Cities constructed during the automobile era are more scattered, while cities where employment is centralized and taxpayers shoulder more infrastructure costs tend to build on a relatively cheaper and more compact scale.
