Projections - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 84

Examples of tangent and secant pro-
jection surfaces.
conformal conic projection, which preserves angles, but not areas. If a pro-
jection preserves areas in the projection by a constant scaling factor, it is
called an equivalent projection. Equivalent projections preserve areas, but not
shapes. The shapes of continents or countries can change in an equivalent
projection, but their areas correspond to the actual areas on the earth (Fig-
ure 4.8, Sinusoidal projection). Projections that preserves distances from one
or two points to other points are called equidistant (Figure 4.8, Stereographic
projection). The projections that preserve directions are called azimuthal ,or
true direction, projections. Directions are only preserved from the center of
the map in azimuthal projections.
Projections that are neither conformal nor equivalent are called compro-
mise projections. They are usually developed to make more graphically pleas-
ing maps and do this by finding a balance between areal and angular distor-
tion (Figure 4.8, Robinson projection).
Some Common Projections, Characteristics, and Uses
With so many projections, it is possible to find a projection for every occa-
sion. Fortunately, for most geographic information uses, the projections are
already determined. The choices for maps, especially maps of large areas,