INTRODUCTION
Digital Elevation Models
The USGS Digital Elevation Model (DEM) data files are digital representations
of cartographic information in a raster form. DEMs consist of a sampled
array of elevations for a number of ground positions at regularly spaced
intervals. These digital cartographic/geographic data files are produced
by the U.S. Geological Survey (USGS) as part of the National Mapping Program
and are sold in 7.5-minute, 15-minute, 2-arc-second (also known as 30-minute),
and 1-degree units. The 7.5- and 15-minute DEMs are included in the large
scale category while 2-arc-second DEMs fall within the intermediate scale
category and 1-degree DEMs fall within the small scale category.
The method of determining DEM accuracy involves computation of the root-mean-square error (RMSE) for linearly interpolated elevations in the DEM and corresponding true elevations from the published maps. Test points are well distributed and representative of the terrain. Collection of test point data and comparison of the DEM to the quadrangle hypsography are conducted by USGS quality-control groups.
Source: USGS EROS Data Center
INTERACTIVE MAP
Click on the thumbnail below to open an interactive ArcIMS map with
Atrazine data.
Map Thumbnail |
Layers
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Notes
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| DEM Louisiana83 |
Click on the thumbnail to open the LIMA web mapping application, then select the Rasters > Elevation Data folders, then click the "DEM Louisiana82" checkbox to display the DEM imagery. |
RELATED LINKS
Related web pages on the Internet:
USGS Digital Elevation Dataset
home page