Digital Elevation Models DEM are data files that include the elevation of the terrain over a specific area, generally at a fixed grid distance over the surface of the earth. The distance connecting each of the grid points will constantly be referenced to some geographical coordinate system. This is usually either latitude-longitude or UTM (Universal Transverse Mercator) coordinate systems. The details of the peaks and valleys in the terrain will be better represented with small grid spacing than when the grid intervals are very large. Elevations at the specific grid point locations are not contained in the file. As a result peak points and valley points not coincident with the grid will not be recorded in the file.











The term Digital Elevation Modeling is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface. A DEM can be represented as a raster (a grid of squares, also known as a height map when representing elevation) or as a vector-based triangular irregular network (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM. DEMs are commonly built using remote sensing services techniques, but they may also be built from land surveying. DEMs are used often in geographic information systems, and are the most common basis for digitally-produced relief maps. The DEM could be acquired through techniques such as photogrammetry, LiDAR, land surveying, etc. While a DSM may be useful for landscape modeling, city modeling and visualization applications, a Digital Terrain Model is often required for flood or drainage modeling, land-use studies, geological applications, and much more. Methods for obtaining Digital elevation data used to create DEMs such as LIDAR,Stereo photogrammetry from aerial surveys, Block adjustment from optical satellite imagery, Interferometry from radar data, Real Time Kinematic GPS, Topographic maps, Theodolite or total station, Doppler radar, Focus variation .Inertial surveys.









Digital Elevation Models (DEMs) are a type of raster GIS layer. Raster GIS represents the world as a regular arrangement of locations. In a DEM, each cell has a value corresponding to its elevation. The fact that locations are arranged regularly permits the raster GIS to infer many interesting associations among locations. One of the most powerful applications of DEMs is adding synthetic hillshading to maps so that the map reader may see the relationship between terrain and other things you may be mapping.








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