Cylindrical

The standard cylindrical (Mercator) gives us minimum distortion around the equator. If one is mapping the temperate zones of the entire earth, it represents a good choice.

Conic

The Conic enables us to move the east/west line of minimum distortion from the equator to any other line of latitude. Choosing a cone that touches the earth at about 36 degrees of north latitude would be a good choice for producing a map of Tennessee. Tennessee is much larger east/west than north/south.

Transverse Cylindrical

The Transverse Cylindrical (Transverse Mercator) produces clean crisp lines in a north/south direction. It is the projection of choice for mapping a state such as New Hampshire. New Hampshire is much larger north/south than east/west.

Azimuthal

When choosing the flat surface, the Azimuthal projection provides minimum distortion in all directions for a limited distance and is the projection used for maps of the polar regions.

Minimizing the projection distortion in a map of a specific region of the Earth is a matter of choosing the right projection. The general rule of thumb is if the greatest extent of the region to be mapped is east/west, the Conic projection should be used. If the greatest extent of the region is north/south, the Transverse Mercator projection should be used. A cylinder (or a cone) can be tilted to obtain clean crisp lines in any specific direction. Such projections exist for the cylindrical case and are referred to as oblique cylindrical projections. For example, the Hotine Oblique Mercator projection is used to map the panhandle of Alaska.

Minimized Using Scale Reduction

We have seen that the degree of projection distortion at any given point on a map depends upon how far away the developed surface is from the surface to be mapped. We have seen that we can get the photographic film closer to the surface being mapped by using different shapes.

There is another technique used in cartography to reduce the overall distance between the photographic film and the surface of the earth for a given region. In the case of a cylindrical projection, imagine the result if we could shrink the cylinder into the Earth just a little bit. Some of the cylinder would be inside the Earth and some would be outside. However, for a specific region of the Earth, the largest distance between the photographic film and the globe will be reduced. Further, there would be two lines where the cylinder actually touched the surface thereby giving us two lines where there is zero distortion. This technique enables us to, in general, get more of the film closer to more of the region which we wish to map.