The systematic part of the terrain surface is characterized either by sharp cracks in the terrain, such as the top or bottom of a road cut, or by characteristic points such as spot depression and spot height. It is usual to use a network that creates sloping triangles or regular quadrants. It would take an endless number of points to describe exactly the random terrain shapes, but these can be described in practice with a network of points. The random (stochastic) elements are the continuous surfaces with continuously varying relief. The terrain surface can be described as compromising of two different elements random and systematic. DEMs are used often in geographic information systems, and are the most common basis for digitally-produced relief maps. DEMs are commonly built using remote sensing techniques, but they may also be built from land surveying. While the term can be used for any representation of terrain as GIS data, it is generally restricted to the use of a raster grid of elevation values. It is also widely known as a digital terrain model ( DTM). Topography of the Andes from a digital elevation modelĪ digital elevation model ( DEM) is a digital representation of ground surface topography or terrain.
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