Geomatics science applied to cartographic heritage and archive sources: a new way to explore the XIX century Gregorian Cadastre of Bologna (Italy), an ante-litteram 3D GIS

Regeneration of cartographic heritage in a digital form offers a new opportunity of preserving and studying historical cartography. Modern digital techniques coming from Geomatics science help in metric analysis of ancient maps and, when integrated with the contribution from other disciplines, can allow specific studies otherwise unachievable. The study subject is the first establishment urban map of the nineteenth century Gregorian Cadastre of Bologna, today kept at the local State Archives. The uniqueness of this cadastral cartography is to be composed by ground-floor maps and separate maps for the single floors above and below; written documentation on land lots completes the cadastre. In the study, digital tools deriving from the integration of geomatic techniques (in particular georeferencing, GIS, 3D modelling) and archive skills are used to deeply analyze this peculiar cadastre, once converted in a digital form and metrically processed. For some test areas, a comparative consultation of the graphical information stored in the georeferenced maps, and the written one in the related cadastral registers is performed; this allows rigorous 3D digital reconstructions of the cadastral properties, and a new thematic visualization. This modern kind of representation turns to be a powerful and expressive tool to deeply analyze the complex nineteenth century arrangement of the city, highlighting some interesting aspects which otherwise would remain invisible. Furthermore, the tool allows users to get information about the Gregorian Cadastre in a simpler way than searching the original documents; this way, moreover, avoiding any damage of the delicate ancient maps.