Geocart Projections

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McBryde-Thomas flat-pole parabolic


Equal area


Meridians: Central meridlan is a straight line 0.48 as long as the Equator. Other meridians are equally spaced parabolic curves, concave toward the central meridian.
Parallels: Unequally spaced straight parallel lines, farthest apart near the Equator. Perpendicular to the central meridian.
Poles: Lines one-third as long as the Equator
Symmetry: About the central meridian or the Equator


True along latitudes 45°30' N. and S. Constant along any given latitude; same for the latitude of opposite sign


Distortion is severe near outer meridians at high latitudes but less than the corresponding distortion on pointed-polar projections. Free of distortion only at latitudes 45°30' N. and S. at the central meridian.


Basis of merged projections by McBryde


Presented by F. Webster McBryde and Paul D. Thomas through the U.S. Coast and Geodetic Survey in 1949

Similar projections

Craster Parabolic projection, equal area with parabolic meridians but with pointed poles and a central meridian that is half the length of the Equator
Putnins P4' projection (1934), equal area with parabolic meridians but with poles and a central meridian that are all half the length of the Equator.
Werenskiold I (1944) is identical to Putnins P4' except for the scale. Putnins P3' projection (1934) has meridians, poles, and Equator identical to those of Putnins P4', but parallels are equally spaced.

Description adapted from J.P. Snyder and P.M. Voxland, An Album of Map Projections, U.S. Geological Survey Professional Paper 1453. United States Government Printing Office: 1989.