Understanding Map Projections

AZIMUTHAL EQUIDISTANT
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.
The center of the projection is 0°, 0°.
DESCRIPTION
The most significant characteristic is that both
distance and direction are accurate from the central
point. This projection can accommodate all aspects:
equatorial, polar, and oblique.
PROJECTION METHOD
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 or the South Pole,
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 a 90 degree angle.
Oblique—The central meridian is straight, but there
are no 90 degree intersections except along the
central meridian.
PROPERTIES
Shape
Except at the center, all shapes are distorted.
Distortion increases 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.
Degrees from center:
15 30 45 60 90
Scale distortion in percent 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—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; for example, 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.
38 • Understanding Map Projections