Polyconic projection class
Polyconic can refer either to a class of map projections or to a specific projection known less ambiguously as the American polyconic projection. Polyconic as a class refers to those projections whose parallels are all non-concentric circular arcs, except for a straight equator, and the centers of these circles lie along a central axis. This description applies to projections in equatorial aspect.
Some of the projections that fall into the polyconic class are:
- American polyconic projection -- each parallel becomes a circular arc having true scale, the same scale as the central meridian
- Latitudinally equal-differential polyconic projection
- Rectangular polyconic projection
- Van der Grinten projection -- projects entire earth into one circle; all meridians and parallels are arcs of circles.
- Nicolosi globular projection -- typically used to project a hemisphere into a circle; all meridians and parallels are arcs of circles.
A series of polyconic projections, each in a circle, was also presented by Hans Mauer in 1922, who also presented an equal-area polyconic in 1935.:248 Another series by Georgiy Aleksandrovich Ginzburg appeared starting in 1949.:258–262
Most polyconic projections, when used to map the entire sphere, produce an "apple-shaped" map of the world. There are many "apple-shaped" projections, almost all of them obscure.
- An Album of Map Projections (US Geological Survey Professional Paper 1453), John P. Snyder & Philip M. Voxland, 1989, p. 4.
- John J. G. Savard. "The Dietrich-Kitada Projection".
- John P. Snyder (1993). Flattening the Earth: Two Thousand Years of Map Projections. ISBN 0-226-76747-7.
- Table of examples and properties of all common projections, from radicalcartography.net
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