Significant Topographic Changes in the United States
The importance of urban development (including building construction and associated road construction) as a human geomorphic process has been recognized as a primary input for calculations of the total amount of material moved by humans. The topographic change polygon dataset includes many features that are the result of earth-moving operations for urban development.
The southern California counties of Orange, San Diego, and Los Angeles are the top ranked counties in terms of area of topographic change polygons labeled as urban/built-up according to the NLCD. Orange County, the top ranked county, contains 72 change polygons (see figure below), most of which appear to be associated with new development. The detected change areas are located in the higher relief portions of the county where cuts, fills, or both are required to reduce the terrain slope enough to allow for housing and commercial building construction.
The next two figures provide examples of where the cut and fill polygons associated with urban development are located on the landscape.