Historical Maps

Maps have to be processed in order to overlay them on the Google Maps. The geodetic coordinate system consists of a datum, a projection, an origin, a unit system and two axis. Google Maps uses WGS84, Mercator projection and a pixel unit system. Most of the maps of the United States are in conical projection

In our case the projection does not have to be exact. For small areas in Molweide projection, for example a simple perspective correction can be sufficient.

A map projection is a process which converts spherical or ellipsoidal surface (3d) to a projection surface (2d). A datum is a set of reference points on the earth's surface (ellipsoid) to define a geographic coordinate system. (Adapted from An introduction to map projections)