The most significant characteristic of the Equidistant Azimuthal projection is that both distance and direction are accurate from the central point. This projection can accommodate all aspects, equatorial, polar and oblique.
Method of Projection - Planar:
The world is projected onto a flat surface from any point on the globe. Although all aspects are possible, the one used most commonly is the polar aspect, in which all meridians and parallels are divided equally to maintain the equidistant property. Oblique aspects centered on a city are also common.
Point of Tangency:
A single point, usually the North Pole or the South Pole, but can be any other point. This point is defined by degrees of latitude and longitude.
Linear Graticules:
Polar: Straight meridians are divided equally by concentric circles of latitude.
Equatorial:
The Equator and the projection's central meridian are linear and meet at 90 degrees.
Oblique:
The central meridian is straight but there are no 90-degree intersections except along the central meridian.
Properties:
Shape: All shapes are distorted except at the center, and increasingly from the center.
Area: Distortion increases outward from the center point.
Direction: True directions from the center outward.
Distance: Distances for all aspects are accurate from the center point outward. For the polar aspect, the distances along the meridians are accurate but there is a pattern of increasing distortion along the circles of latitude, outward from the center.
Limitations:
Usually limited to 90 degrees from the center, although it can project the entire globe. Polar-aspect projections are best for regions within a 30-degree radius because there is only minimal distortion (Roblin).
Degrees from Center: 15 30 45 60 90
% Scale Distortion Along Parallels: 1.2 4.7 11.1 20.9 57
Uses and Applications:
Routes of air and sea navigation. These maps will focus on an important location as their central point and use an appropriate aspect:
Polar aspect: Descriptive polar regions and polar navigation.
Equatorial aspect: Locations on or near the Equator, such as Singapore.
Oblique aspect: Locations between the poles and the Equator, such as large-scale mapping of Micronesia.
If this projection is used on the entire globe, the immediate hemisphere can be recognized and resembles the Lambert Azimuthal projection. The outer hemisphere greatly distorts shapes and areas. In the extreme, a polar-aspect projection centered on the North Pole will represent the South Pole as its largest outermost circle. The function of this extreme projection is that, regardless of the conformal and area distortion, an accurate presentation of distance and direction from the center point is maintained.
