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The American polyconic map projection is a
Table of examples and properties of all common projections
from radicalcartography.net
Map projections {{cartography-stub
The American polyconic map projection is a map projection
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longit ...
used for maps of the United States and regions of the United States beginning early in the 19th century. It belongs to the polyconic projection class
Polyconic can refer either to a class of map projections or to a specific projection known less ambiguously as the American polyconic projection. Polyconic as a class refers to those projections whose parallels are all non-concentric circular ar ...
, 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 Ferdinand Rudolph Hassler
Ferdinand Rudolph Hassler (October 6, 1770 – November 20, 1843) was a Swiss-American surveyor who is considered the forefather of both the National Oceanic and Atmospheric Administration (NOAA) and the National Institute of Standards and Techn ...
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.''Flattening the Earth: Two Thousand Years of Map Projections'', John P. Snyder, 1993, pp. 117-122, . It is not used much these days, having been replaced by conformal projections in the State Plane Coordinate System.
Description
The American polyconic projection can be thought of as "rolling" a cone tangent to the Earth at all parallels of latitude. This generalizes the concept of a conic projection, which uses a single cone to project the globe onto. By using this continuously varying cone, each parallel becomes a circular arc having true scale, contrasting with a conic projection, which can only have one or two parallels at true scale. The scale is also true on the central meridian of the projection. The projection is defined by: : where ''λ'' is the longitude of the point to be projected; ''φ'' is the latitude of the point to be projected; ''λ'' is the longitude of the central meridian, and ''φ'' is the latitude chosen to be the origin at ''λ''. To avoid division by zero, the formulas above are extended so that if ''φ'' = 0 then ''x'' = ''λ'' − ''λ'' and ''y'' = −''φ''.See also
*List of map projections
This is a summary of map projections that have articles of their own on Wikipedia or that are otherwise notable
Notability is the property
of being worthy of notice, having fame, or being considered to be of a high degree of interest, signif ...
References
External links
*Table of examples and properties of all common projections
from radicalcartography.net
Map projections {{cartography-stub