The McBryde-Thomas Flat Polar Quartic Projection is a pseudocylindrical, equal area projection. It was presented by F. Webster McBryde and Paul D. Thomas in 1949. It is primarily used for examples in various geography textbooks, and is sometimes known simply as the Flat-Polar Quartic projection.
The central meridian is a straight line 0.45 as long as the Equator. Other meridians are fourth-order (quartic) curves that are equally spaced and concave toward the central meridian. The parallels are unequally spaced straight parallel lines, spaced farthest apart near the Equator and running perpendicular to the central meridian. The poles are represented by lines one-third as long as the Equator.
Scale is true along latitudes 33°45' N and S, and is constant along any given latitude. Distortion is severe near the outer meridians at high latitudes. This projection is free of distortion only at the intersection of the central meridian with latitudes 33°45' N and S.
The "McBryde-Thomas Flat Polar Quartic" projection has the following parameters:
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Longitude of Origin
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False Easting
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False Northing
Note: Only a spherical form of this projection is used. The semi-major axis of the ellipsoid will be used as the radius of the sphere.