Polyconic

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Polyconic was developed in 1820 by Ferdinand Hassler specifically for mapping the eastern coast of the US. Polyconic projections are made up of an infinite number of conic projections tangent to an infinite number of parallels. These conic projections are placed in relation to a central meridian. Polyconic projections compromise properties such as equal-area and conformality, although the central meridian is held true to scale.

Construction

Cone

Property

Compromise

Meridians

Central meridian is a straight line, but all other meridians are complex curves.

Parallels

Parallels (except the Equator) are nonconcentric circular arcs. The Equator is a straight line.

Graticule spacing

All parallels are arcs of circles, but not concentric. All meridians, except the central meridian, are concave toward the central meridian. Parallels cross the central meridian at equal intervals but get farther apart at the east and west peripheries.

Linear scale

Scale along each parallel and along the central meridian of the projection is accurate. It increases along the meridians as the distance from the central meridian increases (Environmental Systems Research Institute, 1992).

Uses

Used for 7.5-minute and 15-minute topographic USGS quad sheets, from 1886 to about 1957 (Environmental Systems Research Institute, 1992).

Used in slightly modified form for large-scale mapping in United States until the 1950s.

This projection is used mostly for north-south oriented maps. Distortion increases greatly the farther east and west an area is from the central meridian. In the figure below the central meridian is 100°W.

Polyconic Projection of North America

map_projection_polyconic