Map Projections - Spatial Mathematics: Theory and Practice through Mapping - page 193

Regular cylindrical Regular conic

Transverse
cylindrical

Polar azimuthal
(plane)

Oblique
cylindrical

Oblique azimuthal
(plane)

Figure 9.1 Conceptual view of a number of projection types for transforming the grat-
icule to a grid. Source: Snyder, J. P. 1987. Map Projections—A Working Manual, US
Geological Survey Professional Paper 1395. http://pubs.usgs.gov/pp/1395/report.pdf

• Conic . Imagine a cone of paper placed over a globe, tangent to the
globe along one line (small circle). Often the apex of the cone is above
the north geographic pole, creating a visual image with the globe
of an upside-down ice cream cone. The graticule on the sphere is
projected onto the cone that was rolled from a piece of paper. In the
right-hand column of Figure 9.1, the top image shows this concept.
As with the cylinder, the axis of the cone may be inclined at a variety
of angles to the Earth's polar axis.

If the small circle that is common to both the surfaces of the cone and the
sphere is a parallel (line of equal latitude), as it will be if and only if the coni-
cal apex lies on the extended polar diameter of the Earth, then the projection
that results when the cone of projection is unrolled is called a conic projection