Geocart Projections

What is a projection?

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Chamberlin trimetric

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

Classifications

Geocart menu class: Azimuthal
Modified azimuthal
Modified equidistant
Neither conformal nor equal area

Graticule

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

Scale

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

Distortion

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

Usage

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

Origin

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.