DEM's, digital elevation models, are digital models or 3-D representations of a terrains surface. They are a digital file that consists of terrain elevations for ground positions that are calculated at regularly spaced intervals. They used a raster format and their features are tied into a coordinate system, a datum and a map projection. In raster format, the data is recorded, stored and processed in a cell or pixel. The image above is a 3-D sectional representation of the Sahara Desert in southern Tunisia. You can clearly see the elevation changes from the 3-D format and the use of contour lines. As the name implies this style is used to display the elevation of a terrain in digital format.
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