Bipolar Oblique Conic Conformal projection was developed by O.M. Miller and William A. Briesemeister in 1941 specifically for mapping North and South America, and maintains conformality for these regions. It is based upon the Lambert Conformal Conic, using two oblique conic projections side-by-side.
Meridians are complex curves concave toward the center of the projection.
Parallels are complex curves concave toward the nearest pole.
Graticule spacing increases away from the lines of true scale and retains the property of conformality.
Linear scale is true along two lines that do not lie along any meridian or parallel. Scale is compressed between these lines and expanded beyond them. Linear scale is generally good, but there is as much as a 10% error at the edge of the projection as used.
American continents. Examples are Basement map of North America and Tectonic map of North America.
The two oblique conics are joined with the poles 104° apart. A great circle arc 104° 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%. The origin of the coordinates is made 17°15’N, 73°02’W.
See Lambert Conformal Conic for more information.