The amount of impervious surface area in a landscape, primarily associated with transportation facilities (streets, highways, parking lots and sidewalks) and building rooftops, is an indicator of environmental quality. Conversion of rural landscapes to urban and suburban land uses is directly related to increasing amounts of impervious surface area. Imperviousness affects the amount of surface runoff to streams and lakes and is related to the water quality of surrounding lakes and streams, to urban heat island effects, to the aesthetics of landscapes, and to the degradation and fragmentation of natural habitats. This project, in cooperation with the Minnesota Pollution Control Agency and with earlier funding from the Metropolitan Council, has used satellite remote sensing to map the percentage of impervious surface area within the seven-county Twin Cities metropolitan area in 1986, 1991, 1998 and 2002. Over the entire seven-county area the amount of impervious area increased from 9.02 to 12.98% between 1986 and 2002. We are currently finishing statewide classifications for 1990 and 2000. When complete, all of the maps and statistics will be available by county, city, ecoregion, watershed and lakeshed, in a web-based mapping application. Classification of the Landsat Thematic Mapper data enables quantification of the spatial and temporal patterns of impervious surface area over large geographic areas at modest cost.