The distance from the center point to another projected point ρ is the arc length along a great circle between them on the globe. All points along a given azimuth will project along a straight line from the center, and the angle θ that the line subtends from the vertical is the azimuth angle. That point, ( φ 0, λ 0), will project to the center of a circular projection, with φ referring to latitude and λ referring to longitude. (click for detail) Mathematical definition Tissot’s indicatrix applied to the azimuthal equidistant projectionĪ point on the globe is chosen as "the center" in the sense that mapped distances and azimuth directions from that point to any other point will be correct.
Many modern star chart planispheres use the polar azimuthal equidistant projection.Ĭomparison of the Azimuthal equidistant projection and some azimuthal projections centred on 90° N at the same scale, ordered by projection altitude in Earth radii. In France and Russia this projection is named "Postel projection" after Guillaume Postel, who used it for a map in 1581.
The projection appears in many Renaissance maps, and Gerardus Mercator used it for an inset of the north polar regions in sheet 13 and legend 6 of his well-known 1569 map. Īn example of this system is the world map by ‛Ali b. While it may have been used by ancient Egyptians for star maps in some holy books, the earliest text describing the azimuthal equidistant projection is an 11th-century work by al-Biruni. The flag of the United Nations contains an example of a polar azimuthal equidistant projection. A useful application for this type of projection is a polar projection which shows all meridians (lines of longitude) as straight, with distances from the pole represented correctly. It has the useful properties that all points on the map are at proportionally correct distances from the center point, and that all points on the map are at the correct azimuth (direction) from the center point. The azimuthal equidistant projection is an azimuthal map projection. Emblem of the United Nations containing a polar azimuthal equidistant projection. An azimuthal equidistant projection about the South Pole extending all the way to the North Pole. Azimuthal equidistant map projection An azimuthal equidistant projection about the North Pole extending all the way to the South Pole.
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