Geocart Projections

What is a projection?

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Gall stereographic

Classifications

Geocart menu class: Cylindric
Cylindric
Perspective
Neither conformal nor equal area

Graticule

Meridians: Equally spaced straight parallel lines 0.77 as long as the Equator
Parallels: Unequally spaced straight parallel lines, closest near the Equator, but spacing does not increase poleward as fast as it does on the Mercator. Perpendicular to meridians.
Poles: Straight lines equal in length to the Equator
Symmetry: About any meridian or the Equator

Scale

True along latitudes 45° N. and S. in all directions. Constant in any given direction along any other given latitude or the latitude of opposite sign
Changes with latitude and direction but is always too small between latitudes 45° N. and S. and too large beyond them

Distortion

None at latitudes 45° N. and S. Shape, area, and scale distortion increase moderately away from these latitudes but becomes severe at poles.

Other features

Projection is produced geometrically by projecting the Earth perspectively from the point on the Equator opposite a given meridian onto a secant cylinder cutting the globe at latitudes 45° N. and S.

Usage

World maps in British atlases and some other atlases, as a projection somewhat resembling the Mercator but having less distortion of area and scale near the poles

Origin

Presented by James Gall of Edinburgh in 1855 as his Stereographic, which he preferred to his Orthographic (equal-area) and Isographic (equidistant) cylindrical projections presented at the same time and also based on cylinders secant at latitudes 45° N. and S.

Aspects

Only the normal aspect is used.

Other names

Gall Stereographic

Similar projections

Miller Cylindrical projection has different spacing of the parallels, and the line of no distortion is the Equator rather than latitudes 45° N. and S.
B.S.A.M. (Great Soviet World Atlas) projection of 1937 is the same, except that the cylinder is secant at latitudes 30° N. and S.
V.A. Kamenetskiy used an identical projection for Russian population density in 1929, except that the cylinder was made secant at latitudes 55° N. and S.
Guy Bomford of Oxford University in England about 1950 devised a Modified Gall projection, which is like the regular Gall in spacing except that meridians are slightly curved at higher latitudes to decrease scale exaggeration at the poles.
Moir devised “The Times” projection in which the straight parallels are spaced as they are on the Gall projection but the meridians are distinctly curved.

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.