What is the main distinction of a geoid compared to other earth models?

The geoid is a specific model of the Earth's shape that takes into account the variations in gravitational forces exerted by the Earth's mass distribution. Unlike other models, such as a perfect sphere or a mathematical sphere, the geoid is not uniform; it reflects the irregularities in the Earth's gravity field, which are caused by factors like mountains, ocean trenches, and the Earth's rotation. This model is particularly important for understanding sea level and for applications in geodesy, as it provides a more accurate representation of how the Earth's surface relates to mean sea level. The geoid essentially serves as a reference surface from which elevations and depths can be measured, making it an essential concept in both cartography and geographic information systems.