Georeferencing Historical Cartography: a quality control method

The use of historical cartography within a GIS environment to realize long-term change-detection studies of a certain area has become an established and fairly generalized practice. As is well known, the prerequisite condition for such analyses is the thorough rectification of the historical map's digital format. This article offers a methodology for creating a form of “accuracy assessment” for georeferencing executed on a historical map, based on a comprehensible control procedure that can be completed within a reasonable time frame. The fundamental idea is to use a set number of points to measure the gap between their positions on a georeferenced historical map and the reality of the territory. The control procedure creates a series of parameters to be added as metadata on the georeferenced map, constituted by the mean error distance and consequent standard deviation and by the percentage of an area examined on a map, drawn from a control grid superimposed on it.