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Geodesy involves the theory, measurement, and computation of the size, shape, and gravity field of the earth. Modern geodesy is now also concerned with temporal (time) variations in these quantities, notably through contemporary observations of geodynamic phenomena. Geodesy is a branch of applied mathematics that forms the scientific basis of all positioning and mapping.

In relation to GIS, geodesy provides the fundamental framework for accurate positions on or near the earth's surface (georeferencing). Any soundly georeferenced GIS database should be based on appropriate geodetic datums (defined later), and—where applicable—positions displayed in terms of a map projection best suited to the purpose at hand. As such, geodesy underpins GIS in that it provides a sound and consistent framework for the subsequent analysis of spatial data. GIS databases ...

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