Geocart Projections

What is a projection?

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Parameters: Standard parallel


Geocart menu class: Conic
Equal area


Meridians: Central meridian is a straight line. Other meridians are complex curves connecting points equally spaced along each parallel of latitude and concave toward the central meridian.
Parallels: Concentric circular arcs spaced at true distances along the central meridian. The curvature of the central or standard parallel is identical to its curvature on a cone tangent at that latitude.
Poles: Points
Symmetry: About the central meridian


True along the central meridian and along each parallel
Free of all distortion along the central meridian and the central parallel


Frequently used until recently for atlas maps of continents. Used in the ellipsoidal form for topographic mapping of France in the early 19th century.


Developed in rudimentary form by Claudius Ptolemy (about A. D. 100). Further developed by Bernardus Sylvanus in 1511. Used considerably by Rigobert Bonne (1727-95) of France, especially in 1752; the name is taken from him.

Limiting projections

Werner projection if a pole is made the standard parallel
Sinusoidal projection if the Equator is made the standard parallel. The pseudoconic projection thereby becomes a pseudocylindrical projection, but the Bonne formulas must be rewritten.

Similar projection

John Bartholomew combined the Bonne projection with the Equidistant Conic projection with two standard parallels. In his 1942 "Kite" and 1958 "Regional" projections, the Equidistant Conic is used in the north temperate zone, and the Bonne is used south of the Tropic of Cancer in interrupted form. The more northern regions are based on the Bonne ("Kite") and Conic ("Regional") projections. These two projections emphasize land masses, and Bartholomew's 1958 "Lotus" projection emphasizes the oceans by using a southern version of the "Regional" projection.

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.