Polyconic projection class

Class of map projections

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.^[2]

A series of polyconic projections, each in a circle, was also presented by Hans Mauer in 1922,^[3] who also presented an equal-area polyconic in 1935.^[4]^: 248 Another series by Georgiy Aleksandrovich Ginzburg appeared starting in 1949.^[4]^{: 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.^[2]

References

^ An Album of Map Projections (US Geological Survey Professional Paper 1453), John P. Snyder & Philip M. Voxland, 1989, p. 4.
^ ^a ^b John J. G. Savard. "The Dietrich-Kitada Projection".
^ https://pubs.usgs.gov/pp/1453/report.pdf ^{[bare URL PDF]}
^ ^a ^b John P. Snyder (1993). Flattening the Earth: Two Thousand Years of Map Projections. ISBN 0-226-76747-7.

External links

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

Map projection

History
List
Portal

By surface

Cylindrical

Mercator-conformal	Gauss–Krüger Transverse Mercator Oblique Mercator
Equal-area	Balthasart Behrmann Gall–Peters Hobo–Dyer Lambert Smyth equal-surface Trystan Edwards
Cassini Central Equirectangular Gall stereographic Gall isographic Miller Space-oblique Mercator Web Mercator

Pseudocylindrical

Equal-area	Collignon Eckert II Eckert IV Eckert VI Equal Earth Goode homolosine Mollweide Sinusoidal Tobler hyperelliptical
Kavrayskiy VII Wagner VI Winkel I and II

Conical

Pseudoconical

Azimuthal
(planar)

General perspective	Gnomonic Orthographic Stereographic
Equidistant Lambert equal-area

Bonne	Sinusoidal Werner
Bottomley	Sinusoidal Werner
Cylindrical	Balthasart Behrmann Gall–Peters Hobo–Dyer Lambert cylindrical equal-area Smyth equal-surface Trystan Edwards
Tobler hyperelliptical	Collignon Mollweide
Albers Briesemeister Eckert II Eckert IV Eckert VI Equal Earth Goode homolosine Hammer Lambert azimuthal equal-area Quadrilateralized spherical cube Strebe 1995