Chamberlin trimetric projection

The Chamberlin trimetric projection is a map projection where three points are fixed on a sphere and used to triangulate the transformation onto a plane. It was developed in 1947 by Wellman Chamberlin, chief cartographer of the National Geographic Society. Unlike a plane-to-plane triangulation, where three compass circles will intersect at a unique point, the Chamberlin trimetric projection will map compass circles from a sphere in such a way so that each pair of circles will result in distinct points of intersection. Usually a triangle is generated from these intersections and the barycenter is chosen to be the point of mapping.

Therefore, the Chamberlin trimetric projection is not equidistant, not conformal, inequivalent, and not azimuthal. It is not used in situations where absolute accuracy is required. However, it does produce a compromise image which minimizes distortions in area, direction, and distance and therefore gives an excellent overall sense of the area being mapped. For this reason, the projection is popular for large areas in atlases, especially of triangular regions. The National Geographic Society routinely uses this projection for representations of Africa, South America, and Greenland, all of which are notorious for being misrepresented (in area, or distances) in other common projections.

The Chamberlin trimetric projection is inappropriate for mapping the entire sphere.