two-point equidistant

doubly equidistant

Parameters: Anchor point 1, Anchor point 2

Classifications

equidistant

Graticule

Meridians: Complex curves.
Parallels: Complex curves.
Poles: Normally points.
Symmetry: Normally none.

Aspects

Typically oblique.

Limiting forms

If the two central points are identical, the azimuthal equidistant projection results.

Scale

True along a straight line from either of two central points.

Distortion

No points free of distortion.

Usage

Map of Asia by the National Ceographic Society.
Could be used to determine the distance from a ship at sea at a known location from the start and end of a voyage.

Similar projections

Azimuthal equidistant, on which distance is correct from only one point.
Donald Elliptical, developed by Jay K. Donald of the American Telephone and Telegraph Company in 1956. Used by telephone companies to establish long-distance rates, the Donald is a Two-Point equidistant projection specially modified for the ellipsoid and confined to the United States and southern Canada.
Chamberlin Trimetric, an approximate three-point equidistant projection.
Two-Point azimuthal-equidistant, presented by Charles F. Close in 1922, has true azimuths from one point and true distances from a second point to all other points.

Origin

Presented by Hans Maurer (1868-1945) of Cermany in 1919 and Charles F. Close (1865-1952) of England independently in 1921.

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.