geoid
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[geodesy]
A representation of the earth's surface if it were completely covered by oceans, essentially depicting mean sea level. A geoid is an ellipsoid with variations that account for landmass, ocean trenches, and gravitational and centrifugal forces. It is irregular and varies from a perfect sphere by as much as 75 meters above and 100 meters below its surface. Used in geolocation, object, and seismic measurement applications. Also known as the surface of equal gravitational potential.
