Understanding Map Projections

BIPOLAR OBLIQUE CONFORMAL CONIC
DESCRIPTION
This projection was developed specifically for
mapping North and South America. It maintains
conformality. It is based on the Lambert Conformal
Conic, using two oblique conic projections side by
side.
PROJECTION METHOD
Two oblique conics are joined with the poles
104 degrees apart. A great circle arc 104 degrees
long begins at 20° S and 110° W, cuts through
Central America, and terminates at 45° N and
approximately 19°59'36" W. The scale of the map is
then increased by approximately 3.5 percent. The
origin of the coordinates is 17°15' N, 73°02' W
(Snyder, 1993).
display North America and South America only. If
having problems, check all feature types (particularly
annotation and tics) and remove any features that
are beyond the range of the projection.
USES AND APPLICATIONS
Developed in 1941 by the American Geographical
Society as a low-error single map of North and South
America.
Conformal mapping of North and South America as a
contiguous unit.
Used by USGS for geologic mapping of North
America until it was replaced in 1979 by the
Transverse Mercator projection.
LINES OF CONTACT
The two oblique cones are each conceptually secant.
These standard lines do not follow any single
parallel or meridian.
LINEAR GRATICULES
Only from each transformed pole to the nearest
actual pole.
PROPERTIES
Shape
Conformality is maintained except for a slight
discrepancy at the juncture of the two conic
projections.
Area
Minimal distortion near the standard lines, increasing
with distance.
Direction
Local directions are accurate because of
conformality.
Distance
True along standard lines.
LIMITATIONS
Specialized for displaying North and South America
only together. The Bipolar Oblique projection will
40 • Understanding Map Projections