Equidistant conic projection

The world on an equidistant conic projection. 15° graticule, standard parallels of 20°N and 60°N.
The equidistant conic projection with Tissot's indicatrix of deformation. Standard parallels of 15°N and 45°N.

The equidistant conic projection is a conic map projection commonly used for maps of small countries as well as for larger regions such as the continental United States that are elongated east-to-west.[1]

Also known as the simple conic projection, a rudimentary version was described during the 2nd century CE by the Greek astronomer and geographer Ptolemy in his work Geography.[2][3]

The projection has the useful property that distances along the meridians are proportionately correct, and distances are also correct along two standard parallels that the mapmaker has chosen. The two standard parallels are also free of distortion.

For maps of regions elongated east-to-west (such as the continental United States) the standard parallels are chosen to be about a sixth of the way inside the northern and southern limits of interest. This way distortion is minimized throughout the region of interest.

  1. ^ Cite error: The named reference pworld was invoked but never defined (see the help page).
  2. ^ Snyder 1987, p. 111.
  3. ^ Snyder 1993, pp. 10–11.