Mean Sea Level (MSL) serves as the key reference point for measuring elevation and altitude. It represents an equipotential surface of the Earth, as defined by the WGS84 geoid. The Earth’s gravity field isn’t perfect or uniform because its density varies across different regions. This variation arises from factors like magma distribution, mountain ranges, and deep-sea trenches.
If the Earth were a perfect sphere covered entirely with water, the water level wouldn’t be consistent everywhere. Instead, it would fluctuate based on the strength of gravity in each area. The ocean’s surface, if it were in equilibrium—meaning calm and unaffected by wind, currents, or the moon—would create an equipotential surface.
A geoid is a mathematical representation of the Earth, illustrating a smooth yet irregular surface that aligns more closely with the Earth’s gravitational field than the actual crust. Essentially, the geoid is the equipotential surface that best fits global mean sea level when analyzed mathematically.
The World Geodetic System (WGS) provides a standard framework for mapping and navigation. It includes a coordinate system for the Earth and defines the nominal sea level through the geoid. The most recent version, WGS 84, was established in 1984 and updated in 2004. This system remains valid until around 2010 and is the basis for the Global Positioning System (GPS).
