Basics of Map Coordinate Systems Peter DeCurtins take an introductory look at a few common ways to model the shape of the earth, reference geographic location, and represent geographic information with map. Part of our Whiteboard Bloggers Series. Geoid : C.F. Gauss, who first described it, called it the “mathematical figure of the Earth”. It is a smooth but highly irregular surface that can be derived only through extensive gravitational measurements and calculations. This gravity-defined equipotential surface theoretically would coincide with the mean ocean surface of the Earth, if the oceans and atmosphere were in equilibrium, at rest relative to the rotating Earth, and the seas extended through the continents (such as with a series of very narrow canals). The geoid is a much closer approximation of the true shape of the Earth than any reference ellipsoid could provide. Reference Ellipsoid : A mathematically-defined surface that approximates the geoid. Because it is an i...
