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Sprawling over croplands

From Washington, D.C., at the 166th annual meeting of the American Association for the Advancement of Science

Urban sprawl has been grabbing headlines because it lengthens commutes, creates heat islands, and alters local weather (SN: 3/27/99, p. 198). Less attention has focused on what the cities sprawl over. Satellite surveys now indicate that the best croplands are disproportionately giving way to cement and asphalt.

At NASA's Goddard Space Flight Center in Greenbelt, Md., Marc L. Imhoff has been probing the impacts of urban development on photosynthesis. He hunted down developed areas in the United States by examining nighttime illumination as recorded by a military satellite. Imhoff mated these data with daytime satellite images recording surface greenness, an index of plant cover. His group then overlaid these two maps on a third. Prepared by the United Nations, it ranks a location's soil on a 9-point scale denoting its potential to support crops.

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