American polyconic projection

In the cartography of the United States, the American polyconic projection is a map projection used for maps of the United States and its regions beginning early in the 19th century. It belongs to the polyconic projection class, which consists of map projections whose parallels are non-concentric circular arcs except for the equator, which is straight. Often the American polyconic is simply called the polyconic projection.

The American polyconic projection was probably invented by Swiss-American cartographer Ferdinand Rudolph Hassler around 1825. It was commonly used by many map-making agencies of the United States from the time of its proposal until the middle of the 20th century.^[1] It is not used much these days, having been replaced by conformal projections in the State Plane Coordinate System.