Changing visual networks around Besançon: Combining intervisibility and vegetation modeling

International audienceArchaeologists have long considered intervisibility essential to understanding settlement patterns and landscape structure. The idea of intervisibility as a driver stems from the premise that, across epochs and cultures, (in)visibility is manipulated for communication, control and sometimes defense. For these reasons a broad suite of viewshed analyses were explored by archaeologists, primarily using GIS, from the 1980s.Many of these studies suggest that vegetation plays an important role in blocking, altering, and framing sightlines, but these suggestions remain relatively unexplored. The increasing availability of airborne laser scanning (ALS) datasets invites us to revisit these propositions. ALS data allows us to consider -with relative ease- multiple vegetation scenarios in which we vary spatial distributions and canopy structure to understand potential impacts on specific visual networks.The approach illustrated in this paper employs ‘rapid initial visual assessment’ of the elements of intervisibility analyses. Multiple 3D scenes are built using sightline vectors, DTMs, and vegetation models. These scenes allow us to immediately understand the impact of terrain and different vegetation states. This rapid exploratory protocol lets us establish a generalized chronology of the changes in extents of woodlands based on presumed or known visual networks. Because calculations are not computationally expensive, quickly modeling many scenarios is practical- opening the possibility of new approaches to visual networks.In this paper our approach is demonstrated use the ‘ceinture de fortifications’ constructed around Besançon in 19th century. Because the state of forest at the time of construction, and the intentions of the architects to create a visual network are well documented, the ceinture provides an ideal case study. We then consider the visual dynamics of two castles and a citadel, constructed and active in the Medieval and Early Modern periods, with reference to historical evidence for competition and cooperation between their respective communities