a mathematical model of the earth used to calculate the coordinates on any map

a reference system or base from which accurate positions of points on the Earth's surface can be determined

a set of parameters (including axis lengths and offset from true center of the Earth) defining a reference ellipsoid

a simplified mathematical representation of the size and shape of the earth

Land surveyor's term for the height above sea level and the latitude and longitude of a particular point on the ground, also known as coordinates.

An ellipsoid typically defined by eight parameters which establish its dimensions, define its center with respect to the Earth's center of mass and specify its orientation in relation to the Earth's average spin axis and Greenwich reference meridian.

A mathematical model designed to best fit part or all of the geoid. It is defined by an ellipsoid and the relationship between the ellipsoid and a point on the topographic surface established as the origin of datum.

A math model representing the size and shape of the earth (or a portion of it).

A set of parameters defining co-ordinate systems for all or parts of the earth. These datums have been refined and revised over time. NAD 27 is the North American datum for 1927, for example. ED50 is the European datum for 1950, and WGS84 is the World Geodetic System for 1984.

A means of representing the figure of the Earth, usually as an oblate ellipsoid of revolution, that approximates the surface of the Earth locally or globally, and is the reference for the system of geodetic coordinates.

Any point, line, or surface used as a reference for a measurement of another quantity. A model of the earth used for Geodetic calculations. A model of the earth's shape.

A math model depicting the shape and size of the earth or portions of the earth.