In a geographical information system, latitude, longitude, and height are commonly used to represent the location of a point on or near the Earth's surface. The first two, called horizontal coordinates, refer to reference ellipsoid and are known as geodetic latitude (?) and longitude (?). The third coordinate, i.e. height of a point is referenced to the Geoid which is an equipotential surface (level surface) of the Earth closely approximating the mean sea level. The geoid is used as a reference surface for heights (height datum) and can be determined globally and regionally.