The Collignon projection is an equal-area pseudocylindrical map projection

Map projection

A map projection is any method of representing the surface of a sphere or other three-dimensional body on a plane. Map projections are necessary for creating maps. All map projections distort the surface in some fashion...

 first known to be published by Édouard Collignon in 1865 and subsequently cited by A. Tissot in 1881.

For the smallest choices of the parameters chosen for this projection, the sphere may be mapped either to a single diamond, a pair of squares or a triangle.
(Another projection that maps each hemisphere to a square is the quincuncial map).

It is used in the polar areas as part of the HEALPix

HEALPix

HEALPix , an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, can refer to either an algorithm for pixelisation of the 2-sphere, an associated software package, or an associated class of map projections.The HEALPix projection is a general class of spherical projections,...

 spherical projection, which is widely used in physical cosmology

Physical cosmology

Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...

 in making maps of the cosmic microwave background, in particular by the WMAP and future Planck Surveyor

Planck Surveyor

Planck is a space observatory of the European Space Agency and designed to observe the anisotropies of the cosmic microwave background over the entire sky, at a high sensitivity and angular resolution...

space missions.

External links

• Pseudocylindrical Projections: Collignon Projection, Carlos A. Furuti
• Projection COLLIGNON à méridiens et parallèles rectilignes, Manuel Luque, Giuseppe Matarazzo
• An interactive Java Applet to study the metric deformations of the Collignon Projection.