A projection is a geometric means of constructing a map of a
sphere (the earth for example) on a flat piece of paper. True projections are
generated by imagining a point source of light shining through a transparent
globe onto a flat surface. The paper may be considered as being rolled into a
cylinder, giving rise to the common Mercator projection and relatives.
Or it can be rolled into a cone, producing conic projection. Or it can
be flat, producing an azimuthal projection. If the projection plane is
located in space (for example at the position of a satellite), the map is
orthographic. This latter is used by WinOrbit for the
Not all maps are true projections. The map used by the
is not. It is called an "equirectangular" map, since all points in the
spherical coordinate system (latitude/longitude) are mapped uniformly (equally
spaced) to a rectangular sheet. This is in contrast to the Mercator
projection, where points near the poles project to points on the map infinitely
far from the equator.