The rapidly expanding urban areas of the world constitute an environmental challenge for the 21st century that requires both new analytic approaches and new sources of data and information. Management of the urban environment must consider phenomena at three scales, including the physical environment within cities, environmental systems consisting of cities and their regional hinterlands, and the environmental implications of the global network of megacities. Increasing availability of remotely sensed observations and a variety of other geospatial information could facilitate the development of new tools and approaches for understanding the urban environment. These new applications should take advantage of the special characteristics of remotely sensed data, including their broad spatial coverage, their capacity for routine and unobtrusive updating and their ability to provide self-consistent measurements of critical physical properties that would be difficult or expensive to obtain in situ. In many cases, using remote sensing data to measure and monitor urban environmental conditions will be more straightforward than using them for urban planning purposes, where traditional sources of governmental and private sector data are more easily obtained and understood. In developing countries, however, remote sensing may provide fundamental observations of urban growth and environmental conditions that are not available from other sources. (C) 2003 Elsevier Science Ltd. All rights reserved.
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