A horizontal datum is a collection of specific points on the Earth’s surface that have been accurately identified according to their precise northerly or southerly location (latitude) and easterly or westerly location (longitude). To create the network of horizontal positions, surveyors marked each of the positions they had identified with a brass, bronze, or aluminum disk known as a survey benchmark. Because surveyors wanted to see one marked position from another, the benchmarks were usually placed on mountaintops or at high elevations. If they were on flat land, surveyors would have towers built to help locate them. In order to create a horizontal datum, these monument locations were connected using mathematical techniques like triangulation. The result of triangulation from the unified network of survey monuments was North American Datum of 1927 (NAD 27) and later the more accurate NAD 83, which is still used today. NAD 27 and NAD 83 provide a frame of reference for latitude and longitude locations on Earth. What is a Horizontal Datum? A horizontal (geometric) datum (or reference frame) forms a basis for computations of horizontal positions on the Earth. Real world objects are defined by coordinate systems. Various coordinate reference systems exist. In each [...]
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The post What is a Horizontal Datum Reference Frame? appeared first on GIS Geography.
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