There is an assumption that the surface contains sufficient vertical relief that a flow path can be determined. The hydrologic analysis tools are designed to model the convergence of flow across a natural terrain surface. Again, this is most noticeable on integer data in flat areas. This can increase as much as 5 percent for a 3-arc-second DEM.ĭEMs may also contain noticeable striping artifacts, a result of systematic sampling errors when creating the DEM. It is not uncommon to find 1 percent of the cells in a 30-meter-resolution DEM to be sinks. This can be particularly troublesome in areas of low vertical relief.
Another common cause of sinks results from storing the elevation data as an integer number.
The number of sinks in a given DEM is normally higher for coarser-resolution DEMs. Digital Terrain Model (DTM) A continuous model of ground-level land surface, represented by a digital raster grid with each grid cell holding an elevation value. Learn more about removing or filling sinks.Sinks, being areas of internal drainage, prevent downslope flow routing of water. These are more commonly natural features and are less detrimental to the calculation of flow direction.Įrrors such as these, especially sinks, should be removed before attempting to derive any surface information. Likewise, a spike, or peak, is an area surrounded by cells of lower value. Some of these may be natural, particularly in glacial or karst areas (Mark 1988), although many sinks are imperfections in the DEM. A sink is an area surrounded by higher elevation values and is also referred to as a depression or pit. A digital terrain models (DTMs) is a continuous surface that, besides the values of height as a grid (known as a digital elevation modelDEM), also consists of other elements that describe the topographic surface, such as slope or skeleton (Podobnikar, 2005). Visualization of a raster DEM surface.Įrrors in DEMs are usually classified as either sinks or peaks. Other factors affecting accuracy are data type (integer or floating point) and the actual sampling of the surface when creating the original DEM. The accuracy of this data is determined primarily by the resolution (the distance between sample points). This data is used as input to quantify the characteristics of the land surface.Ī DEM is a raster representation of a continuous surface, usually referencing the surface of the earth. DTMs are created by integrating data obtained from a wide range of techniques including remote sensing and land surveying. The most common digital data of the shape of the earth's surface is cell-based digital elevation models (DEMs). A Digital Terrain Model (DTM) is a continuous representation of a ground surface landform that is commonly used to produce topographic maps.
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