Significant Topographic Changes in the United States
Tabulation of Statistics Characterizing the Extent of Topographic Change
The final delineation of topographic change polygons included 5,263 distinct features, representing both cuts (decreased elevations) and fills (increased elevations). In addition, 364 polygons outline areas of reservoir construction or expansion, or other similar hydrologic land uses. Each of these polygons has numerous attributes that describe the specific surface modification, such as area and volume, and these characteristics are important for analyzing the local impacts of the change on the landscape.
Also important are national and regional scale summaries of the location and extent of topographic changes. To provide such information, summary statistics were tabulated for different subdivisions and accounting units, including states, counties, ecoregions, watersheds, quadrangle base maps, and 1x1-degree tiles. The figure below summarizes the overall data processing procedure that led to the final delineation of change areas and the accumulation of area-based summary statistics.