Two-point equidistant projection

In this two-point form, two locus points are chosen by the mapmaker to configure the projection.

[3] The projection has been used for all maps of the Asian continent by the National Geographic Society atlases since 1959,[4] though its purpose in that case was to reduce distortion throughout Asia rather than to measure from the two loci.

The Chamberlin trimetric projection is a logical extension of the two-point idea to three points, but the three-point case only yields a sort of minimum error for distances from the three loci, rather than yielding correct distances.

Tobler extended this idea to arbitrarily large number of loci by using automated root-mean-square minimization techniques rather than using closed-form formulae.

[6] The projection can be generalized to an ellipsoid of revolution by using geodesic distance.

Two-point equidistant projection of Eurasia . All distances are correct from the two points (45°N, 40°E) and (30°N, 110°E).
Two-point equidistant projection of the entire world with Tissot's indicatrix of deformation. The two points are Rome, Italy and Luoyang, China.