In consideration of the growing interest in urban space studies, the ALPAGE project (ALPAGE is a French acronym for « diachronic analysis of the Paris urban area: a geomatic approach ») aims at producing data and tools to understand the long term relationships between spaces and societies in Paris.

This project is a three year research program funded by the French National Research Agency (ANR) and it involves the work of 4 laboratories with the collaboration of various partners : LAMOP (project leader), ArScAn, LIENSs, L3i, COGIT, IRHT, the Parisian topography centre, APUR.

The above have come together to collaborate on building a Geographic Information System (GIS) for the Parisian area in the preindustrial period. The creation of such a GIS enables to reconstruct the oldest parcel plan of Paris – the Atlas made by Vasserot between 1810-1836 – and to spatialise historical data from the Middle Ages and modern times (walls, aristocratic mansions, sewers, centennial floods, manors, parishes, etc.). When linked with the old urban fabrics, these data show the diachronic structure of the urban morphology. During the project, the 910 urban block plans of the Vasserot atlas (the oldest parcel plans of Paris) have been thus georeferenced and vectorised. As a result of the active collaboration between historians, geomaticians and computer scientists specialised in automatic vectorisation, this co-production of spatial reference data has allowed the project to take into account the natural and social dimensions of the Parisian urban space.

This work has firstly allowed us to study the geometrical characteristics of parcels through different criteria including; density, shape diversity, and the geometric orientations of the road network and of the parcels. These identified morphological characteristics are then explained by social practices that redefine these shapes over a long term period.

Secondly, the spatial dimension of these historical vectorised objects has been analysed : influence of walls and road network on the parcels, inheritance of past flows on the feudal domains and the sewers.

Thirdly, to improve the understanding of Vasserot's data, plans dated from 1300 to 1380, have also been georeferenced to allow for the comparison and confrontation with medieval texts. Thus, the geocoding on the Vasserot's road system of the taxpayers of the Parisian royal tax in 1300 has been possible.

Finally, an original development of the project, unplanned in its beginning, has been to provide all this new knowledge to everyone through a digital webmapping platform. Data co-produced by researchers involved in the ALPAGE project are now freely visible and stackable with current parcel data obtained by agreement with the Paris planning agency. This webmapping platform may meet certain expectations of members of the civil society that have emerged during the project, such as redefining the scope of protection of the Marais according to the shape of the wall of Charles V. More information about the ALPAGE project is available online: http://lamop.univ-paris1.fr/alpage and http://websig.univ-lr.fr/alpage_public/flash/.