[map projections]
A pseudo-conic, compromise map projection that is neither strictly conformal nor equal-area, shown in equatorial aspect with parallels that are nonconcentric circular arcs—other than a straight equator. The centers of the circular arcs lie along a central axis. Polyconic means many cones, referring to the construction method of projecting a map onto multiple cones, each tangent aligned to a distinct parallel of latitude. The equator and central meridian are straight and perpendicular, but all other meridians are complex curves; the parallels are arcs of non-concentric circles. The polyconic projection minimizes distance distortion along the central meridian and parallels; shape and area distortion increases significantly away from the center. Common polyconic projections include the American polyconic, the rectangular polyconic, and latitudinally equal-differential polyconic projections. This projection was developed by Swiss-American cartographer and surveyor Ferdinand Rudolph Hassler (1770–1843) for the U.S. Coast Survey.