USGS - science for a changing world

Significant Topographic Changes in the United States

Tabulation of Statistics Characterizing the Extent of Topographic Change

Data Processing Methods
Data Processing Methods and Procedures

SRTM NED Vertical Differencing

Accuracy Assessment of Elevation Data

Significant Change Thresholds

Filtering of Elevation Difference Mask to Identify True Topographic Changes

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.

Flow diagram of the overall data processing procedure that resulted in a delineation of topographic surface changes across the conterminous United States
Flow diagram of the overall data processing procedure that resulted in a delineation of topographic surface changes across the conterminous United States.

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