Walking through historical maps of Venice

The mapping and GIS Laboratory of the University IUAV of Venice owns several digital copies of historical maps, some of which concern the city of Venice, form the view by De Barbari to the most recent orthophotos. Even the most careful analysis of an historical map rarely -and almost never easily- allows the automatic individuation of correspondences between points/places and modern reality. In this respect, the main difficulty is the impossible application of transformation formulas, in order to link, in a one-to-one way, a point of the historical map and a point detected inside a known reference system. The purpose of this work is to suggest an adequately reliable methodology in order to allow an immediate and good evaluation of positions on the historical map that correspond to localizations on modern ones, and vice versa. The modern map represents the common ground to evaluate the correspondences among paired points on the ancient maps. This correspondence is calculated in real time and the points are used for the individuation of paths on different maps. The methodology is based on the digitization of some points easily detectable on the first map (reference) and on the historical one. Using these points, a Delaunay triangulation is calculated. Through the correspondent triangles it is possible to obtain, with a good accuracy, the position of every point on the two maps. The results of this study can be visualised for the development of a web application both for mobile systems (smartphones / tablets) –exploiting the availability of their localization sensors (GPS)- and for PC, through the interface offered by browsers. Both of these approaches use the access to map services specifically created for every historical map.