Geocart Projections

What is a projection?

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two-point azimuthal

doubly azimuthal

orthodromic

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McCaw

Immler

Parameters: Anchor point 1, Anchor point 2

Classifications

Geocart menu class: Azimuthal
Modified azimuthal
Neither conformal nor equal area

Graticule

Meridians: Straight lines
Parallels: Equator is straight. Other parallels are ellipses, parabolas, or hyperbolas.
Poles: Points (if shown)
Symmetry: Normally none

Scale

Varies considerably. Projection should not be used for measuring distance

Distortion

Direction is correct to all other points from two central points at which there is no distortion.

Other features

Great circles are shown as straight lines. This projection can be obtained by compressing a Gnomonic projection in the direction parallel to the line joining the two central points.

Usage

Could be used to locate a ship at sea, for example, if the exact location of two radio transmitters and the direction from the ship to the transmitters are known

Origin

Presented by Hans Maurer (1868-1945) of Germany in 1914 and Charles F. Close (1865-1952) of England independently in 1922

Aspects

Typically oblique

Other names

Doubly Azimuthal
Orthodromic
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McCaw Immler

Limiting forms

If the two central points are identical, the Gnomonic projection results.

Similar projections

Gnomonic, which can be compressed as described above to produce the Two-Point Azimuthal projection

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.