Datum, Ellipsoid, Rhumb Line, Secant, Spheroid, Tangent and other useful terms in Map Projection

Datum—A reference for position on the surface of the Earth. In surveying, a datum is a reference system for computing or correlating the results of surveys. There are two principal types of datums: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted…

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