Polyconic

Description

The name of this projection translates into "many cones". This refers to the projection methodology. This affects the shape of the meridians. Unlike other conic projections, the meridians are curved rather than linear.

Projection method

More complex than the regular conic projections, but still a simple construction. This projection is created by lining up an infinite number of cones along the central meridian. This projection yields parallels that are not concentric. Each line of latitude represents the base of its tangential cone.

Lines of contact

Many lines; all parallels of latitude in the projection.

Linear graticules

Central meridian of the projection and the equator.

Properties

Shape

No local shape distortion along the central meridian. Distortion increases with distance from the central meridian; thus, east–west distortion is greater than north–south distortion.

Area

Distortion in area increases with distance from the central meridian.

Direction

Local angles are accurate along the central meridian; otherwise, they are distorted.

Distance

The scale along each parallel and along the central meridian of the projection is accurate. Distortion increases along the meridians as the distance from the central meridian increases.

Limitations

Distortion is minimized on large-scale maps, such as topographic quadrangles, where meridians and parallels can be drawn in practice as straight-line segments. Producing a map library with this kind of map sheet is not advisable because errors accumulate and become visible when joining sheets in multiple directions.

Uses and applications

Used for 7^1/2 and 15 minute topographic USGS quad sheets, from 1886 until approximately 1957.

Some new quad sheets after this date have been falsely documented as polyconic. The present projection for east–west State Plane Coordinate System zones is Lambert conformal conic and Transverse Mercator for north–south state zones.

Learn more about the State Plane Coordinate SystemLearn more about the Lambert conformal conic projectionLearn more about the Transverse Mercator projection

Parameters

Desktop

• False Easting
• False Northing
• Central Meridian
• Latitude of origin

Workstation

• Longitude of Central Meridian
• Latitude of projection's origin
• False Easting (meters)
• False Northing (meters)