Geocart Projections

What is a projection?

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Chamberlin trimetric

Parameters: Anchor point 1, Anchor point 2, Anchor point 3


Modified azimuthal
Modified equidistant
Neither conformal nor equal area


Meridians: Complex curves
Parallels: Complex curves
Poles: Points
Symmetry: Normally none


Approximately correct from three selected widely spaced points on map to any other point on map. Cannot be exactly correct.


Low distortion throughout map if three source points are properly placed near map limits


Atlas maps of continents by the National Geographic Society and some other atlas publishers


Presented by Wellman Chamberlin (1908-76) of the National Geographic Society in 1946

Similar projections

Azimuthal Equidistant projection; true distance and direction from one point
Two-Point Equidistant projection; true distance but not direction from two points

Description adapted from J.P. Snyder and P.M. Voxland, An Album of Map Projections, U.S. Geological Survey Professional Paper 1453. United States Government Printing Office: 1989.