Abstract: Methods and apparatus are provided for referencing a map to the coordinate space of a positioning system, such as a GPS system. For each of a number of real-world positions (X1, X2, X3), the location (LP1, LP2, LP3) of the real-world position in a coordinate space of the map, is associated with a location(LG1, LG2, LG3) in the coordinate space of the positioning system determined by taking at least one positioning-system reading at the real-world position (X1, X2, X3). Using these associated locations, a master transform is determined for converting relative location information between the coordinate spaces. The relative location information is information that serves to specify a location relative to the already-known locations and can take the form of displacement vector information.