GIS Dictionary

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  1. [geodesy] The reference specifications of a measurement system, usually a system of coordinate positions on a surface (a horizontal datum) or heights above or below a surface (a vertical datum).
  2. [remote sensing] In imagery, the origin and orientation of lines on a surface. Datums are used as part of a coordinate reference system to provide a frame of reference when measuring location on the Earth's surface.
  3. [coordinate systems] A collection of very accurate control points used for georeferencing map data so that it aligns with the geodetic latitude and longitude coordinate system; a standard position of level that measurements are taken from.

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