The ALARIC project (Incremental Urban Change Research Project) is dedicated to the production of geo-historical information concerning two formerly industrial cities of the Lyon-Saint-Etienne region (19 th and 20 th century). The exploration of the incremental nature of urban change implies identifying when certain historical processes took place, such as the shift from one-off to systematic construction and changes in urban planning strategies. Specifically, the case study investigates the emergence of local urban projects to compare the transformation processes of the urban fabric and to specify the pace of urban change. Historical records will be accessed through a virtual mapping environment based on the temporal reconstitution of cities in two dimensions, and sometimes for special cases in three dimensions. This paper presents methodological principles to reconstruct former cities in order to inquire urban change and requirements for effective sharing of hypotheses on the various states of the past urban landscape and associated transformation processes.