Small urban watersheds are difficult to characterize in terms appropriate to ecological assessment They are typically larger than the study areas common to ecological assessments, typically measuring in tens of square kilometers in area, even for a small urban stream. They are also more variable and fragmented than natural ecosystems, since they reflect socioeconomic and historical, as well as natural, factors. We have traditionally relied on land use/land cover classifications to characterize such areas, but these record a mixture of natural and socioeconomic variables, and they typically reflect neither the high diversity nor the extreme fragmentation of the urban environment. Doan Brook is a small urban stream on the east side of Cleveland, Ohio. Thematic Mapper (TM) and ½-m resolution Digital Aerial Photography were used together to characterize its roughly 60 km2 area in terms of ecologically meaningful gradients such as percent canopy closure and percent perviousness of the ground. Field checking was used to verify the consistency of the class definition and to correct the parameters. In the process, we found several patterns with ecological significance that would have been overlooked in a more standard classification of the satellite image. The approach used in this study provides an alternative to land-cover analysis that may be broadly applicable to environmental assessments in urban areas, including ecological simulation modeling, assessment of park resources, and analysis of the environmental change in heterogeneous regions.