Georeferencing of an XVIII century technical map of Bologna (Italy)

The study focuses on an eighteenth century map of Bologna, made by the two surveyors G. Monari and A. Laghi. The map represents the first example of a map of Bologna deriving from a general survey of the city, and the first example of flat topographical representation of the city. A digital copy of the map derives from high quality scanning of the original document, which is kept today at the National Archive of Bologna. The study aims at testing the metric quality of this map, according to its original technical function. The georeferencing of the map allowed an assessment of map deformations, a comparison with the present situation and with other maps of the same historical period. The comparison, made by means of mutual overlay of the maps in a GIS environment and measurement tests concerning street width and area, proved the high accuracy of the analysed map.