Understanding Map Projections

ORTHOGRAPHIC
PROPERTIES
Shape
Minimal distortion near the center; maximal
distortion near the edge.
Area
The areal scale decreases with distance from the
center. Areal scale is zero at the edge of the
hemisphere.
Direction
True direction from the central point.
Central meridian is 0°, and latitude of origin is 90° S.
DESCRIPTION
This perspective projection views the globe from an
infinite distance. This gives the illusion of a threedimensional
globe. Distortion in size and area near
the projection limit appears more realistic to our eye
than almost any other projection, except the Vertical
Near-Side Perspective.
Distance
The radial scale decreases with distance from the
center and becomes zero on the edges. The scale
perpendicular to the radii, along the parallels of the
polar aspect, is accurate.
LIMITATIONS
Limited to a view 90 degrees from the central point,
a global hemisphere.
USES AND APPLICATIONS
Uses of this projection are aesthetic more than
technical. The most commonly used aspect for this
purpose is the oblique.
PROJECTION METHOD
Planar perspective projection, viewed from infinity.
On the polar aspect, meridians are straight lines
radiating from the center, and the lines of latitude are
projected as concentric circles that become closer
toward the edge of the globe. Only one hemisphere
can be shown without overlapping.
POINT OF CONTACT
A single point located anywhere on the globe.
LINEAR GRATICULES
All aspects—The central meridian of the projection.
Equatorial aspect—All lines of latitude.
Polar aspect—All meridians.
74 • Understanding Map Projections