Due to equatorial bulge, there is debate as to which of the summits of Mt.

Less commonly, elevation is measured using the center of the Earth as the reference point. The resolution of the gridded data varies from true 2-minute for the Atlantic, Pacific, and Indian Ocean floors and all land masses to 5 minutes for the Arctic Ocean floor. A Mercator projection was used for the world image, which spans 390° of longitude from 270° West around the world eastward to 120° East latitude coverage is ☘0°. Assumed illumination is from the west shading is computed as a function of the east-west slope of the surface with a nonlinear exaggeration favoring low-relief areas. This image was generated by NOAA from digital data bases of land and sea-floor elevations on a 2-minute latitude/longitude grid (1 minute of latitude = 1 nautical mile, or 1.853 km). Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface. The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic system, vertical datum).