1. A method comprising: enabling a user to visually identify geo-coordinates on a source map that correspond with known geo-coordinates on a reference map; using the visually identified geo-coordinates to determine an approximate coordinate transform relating to geo-coordinate relationships between geo-coordinates on a source map and geo-coordinates on an online reference map, said reference map having images being formed by a plurality of tiles; using the approximate coordinate transform to transform an image of the source map to form an image of a modified source map having geo-coordinates that substantially align with corresponding geo-coordinates on the reference map.