4.3 FROM SPACE SYNTAX TO VISIBILITY GRAPH ANALYSIS The original concept behind Visibility Graph Analysis (VGA), developed by Alasdair Turner and Alan Penn at University College of London between the late 1990 and the early 2000, starts from two strands of thought. On one hand there was the theory of space syntax developed by Hillier and Hanson, which we exploited in its basic concepts in the previous chapter. On the other hand there was isovist analy-
sis, independently developed by Benedikt (1979). He created maps of properties of the visual field at points within plans of buildings, and then he drew contours of equal visual area within the plan and called the resulting map an isovist field. Benedikt believed that these maps would give an insight on how people navigate the building. Since closely packed contours would indicate rapidly changing visual field, he reasoned that these would indicate decision points within the building (Turner, Doxa, et al. 2001). Since Benedikt had theorized that isovist fields would correspond to movement patterns of people and Hillier et al have shown that lines through the spaces – axial lines – does correspond with movement pattern within space, it was decided to combine isovist fields with space syntax to provide a measure of how well integrated isovists themselves are within a plan of an environment (Turner 2004) (Turner e Penn 1999). The methodology was later formalized more simply as Visibility Graph Analysis in Turner et al. (2001). In VGA, a grid of points is overlaid to the plan; a graph is then made of the points, where each point is connected to every other point that it can see. The visual integration of a point is based on the number of visual steps it takes to get from that point to any other point within the system. The idea was that all possible locations 140