Polyconic Projection

 

World Map

Polyconic Projection

Central Longitude: 0

Central Latitude: 0

 

Projection Characteristics

The Polyconic projection is useful for maps of continental or smaller regions. Generally, this projection is not used for world maps due to extreme distortion at any significant distance from the center of the projection. Only the central meridian is distortion-free. Notice in the sample map shown above that Africa is relatively undistorted, but the rest of the world is barely recognizable. Scale is true along the central longitude and along each parallel.

 

Projection Parameters

Parameter

Description

Name

Specifies the units used in the map.

Scale

Specifies the unit scale of the projected map, relative to meters. For example, a scale of one means one unit in the projected map equals one meter; a scale of two means two units in the projected map equal one meter; etc.

False Easting

Specifies the false easting, or horizontal offset, of the projected coordinates, in meters. False Eastings and False Northings are added to the underlying "projected" coordinates as a way to arbitrarily offset their internal XY coordinates after the projection. Unless you have a reason for using these offset values, do not use them. These values do not affect the latitude/longitude coordinates for the map, only the internal coordinates used to plot the map on the screen. If you use False Easting and False Northing offsets for a map, any subsequent boundaries you append to the map must also use these same offsets if you want the imported boundaries to be drawn in the correct relative position to the existing boundaries.

False Northing

Specifies the false northing, or vertical offset, of the projected coordinates, in meters. See above.

Central Longitude

Specifies the central longitude of the projection in degrees. The Central Longitude value typically should be defined as the longitudinal center of the map you are going to produce.

Central Latitude

Specifies the central latitude of the projection in degrees. The Central Latitude value typically should be defined as the latitudinal center of the map you are going to produce.

 

 

See Also

Introduction to Map Projections

Types of Projection

Characteristics of Projections

Datums

Ellipsoids

Projection References