Another model that can represent a spherical surface is the cone. A cone is round horizontally, but since it is flat vertically it is also developed. Just cut it on a vertical line and it will be perfectly flat.

To visualize this, we take some photographic film, make a cone and place it on the Earth.

Notice the clean crisp lines now follow a certain line of latitude around the earth; the parallel of latitude at which the photographic cone actually touched the surface of the Earth. As we proceed either north or south from this parallel of latitude, the lines start to get fuzzy and soon disappear altogether.

These are the three forms of map projections: the Azimuthal, the Cylindrical (Mercator), and the Conic. These three forms represent the techniques or projections used in almost all mapping. Now, we will look at some common variations of these forms.