Description
The polyconic projection is also known as American polyconic or ordinary polyconic projection. The name translates into "many cones," and it is created by lining up an infinite number of cones along the central meridian. This affects the shape of the meridians. Unlike other conic projections, the meridians are curved rather than straight. The projection is neither conformal nor equal-area. It is appropriate for regions of predominant north-south extent.
The projection was developed by Ferdinand R. Hassler in 1820. It is available in ArcGIS Pro 1.0 and later and in ArcGIS Desktop 8.0 and later.
Projection properties
The subsections below describe the polyconic projection properties.
Graticule
This is a polyconic projection. The equator and the central meridian are projected as two perpendicular straight lines. All other meridians are complex curves, equally distributed along the equator and each parallel of latitude and concave toward the central meridian. All the parallels are nonconcentric circular arcs, equally distributed along the central meridian. The poles are presented as points. The graticule is symmetric across the equator and the central meridian.
Distortion
The polyconic projection is neither conformal nor equal-area. It generally distorts shapes, areas, distances, directions, and angles. The central meridian is free of distortion. The scale along each parallel and along the central meridian of the projection is accurate. Distortion increases with distance from the central meridian. The east-west distortion is greater than north-south distortion. The projection produces considerable distortion toward the edge of the map. Distortion values are symmetric across the equator and the central meridian.
Usage
The polyconic projection is not recommended for regional maps. Because there is no distortion along the central meridian, the projection is appropriate for regions of predominant north-south extent. It was used for topographic USGS quad sheets from 1886 until approximately 1957.
Parameters
Polyconic parameters are as follows:
- False Easting
- False Northing
- Central Meridian
- Latitude Of Origin
Sources
Snyder, J. P. (1987). Map Projections: A Working Manual. U.S. Geological Survey Professional Paper 1395. Washington, DC: United States Government Printing Office.
Snyder, J. P. (1993). Flattening the Earth. Two Thousand Years of Map Projections. Chicago and London: University of Chicago Press.
Snyder, J. P. and Voxland, P. M. (1989). An Album of Map Projections. U.S. Geological Survey Professional Paper 1453. Washington, DC: United States Government Printing Office.