Georeferencing means that the internal coordinate system of a map or aerial photo image can be related to a ground system of geographic coordinates. For historical maps, this can be a complicated process due to the lack of landmarks, cities, and creativity of map makers.

Researchers are able to use the georeferenced data file with specialized software (like ArcGIS) to combine or compare this data with that currently available. The latter can be used to analyze the changes in the features under study over a period of time.