Earth flattening

Earth flattening (also called oblateness) describes the geometric compression of the Earth along its rotation axis, resulting in an equatorial radius that is slightly larger than the polar radius. This shape is primarily caused by the Earth’s rotation and the resulting centrifugal force. In geodesy, Earth flattening is a fundamental parameter in defining reference ellipsoids, which approximate the Earth’s figure and serve as the basis for coordinate systems, height determination, satellite orbit computation, and the realization of global geodetic reference frames.