Polyconic projection class explained

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.^[1]

Polyconic projections

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,^[2] who also presented an equal-area polyconic in 1935.^[3] Another series by Georgiy Aleksandrovich Ginzburg appeared starting in 1949.^[3]

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.^[4]

See also

• List of map projections

External links

• Table of examples and properties of all common projections, from radicalcartography.net

Notes and References

1. An Album of Map Projections (US Geological Survey Professional Paper 1453), John P. Snyder & Philip M. Voxland, 1989, p. 4.
2. https://pubs.usgs.gov/pp/1453/report.pdf
3. Book: Flattening the Earth: Two Thousand Years of Map Projections. John P. Snyder. 1993. 0-226-76747-7.
4. John J. G. Savard."The Dietrich-Kitada Projection".