A historical GIS for the comparison of past and present views: Bologna, yesterday and today.

Digital regeneration of ancient cartography is an interesting way to allow new chances of viewing and using its historic and geographic information, by modalities that cannot apply to analogue supports. In particular, the creation of a HGIS (Historical Geographic Information System) is a way to make ancient maps suitable for a wide range of applications, from land management to researches on landscape and urban development, from archival researches to tourism promotion. The present study aims to demonstrate the usefulness of GIS tools to collect and link together historical maps and other archive data, e.g. drawings and photos. Some eighteenth and nine-teenth century maps of Bologna were georeferenced and used as a base for a HGIS, together with the current cartography. In order to enrich the environment with historical views of the city, the GIS was populated with a great number of historical pictures (drawings, engravings, photos, postcards), each one linked to the relative historical map by means of a hotspot (rep-resenting the viewpoint from which the picture was probably taken). Together with each his-torical picture, a current photo of the city, taken from the same point of view, can be retrieved and visualized, in order to compare the ancient portrait of the city with its present-day appear-ance. This HGIS, providing a simple and interactive use, offers a new look at the ancient and modern city, turning to be a useful tool for researchers, historians and archivists who recon-struct the evolution of the city, as well as common people interested to rediscover in a unusu-al way the history of Bologna.