Viraph: exploring the potentials of visibility graphs and their analysis

Background: Visibility Graph Analysis (VGA) is a space syntax method for quantifying some socio-spatial properties of the built environment by mapping the floor plan into a grid. Presently, VGA mainly relies on mean values of the measures while the individual room-to-room ("interspatial") relations are not considered or achievable by the common VGA software - depthMapX. Methods: A new software package, Viraph, is developed using a weighed Dijkstra algorithm to calculate depths. The floor plan is mapped into convex areas to increase the speed of calculation. The interspatial relations are calculated by averaging the point-to-point depths in-between. Results: The effectiveness of Viraph is demonstrated through a case study, which compares the houses from the late Victorian era with Wright's Prairie style with a detailed analysis of Francis Little House (designed in 1902). In summary, Viraph has showed a significantly higher calculation speed for VGA, and capability of capturing some socio-spatial relations of the styles by measuring the interspatial depth. Conclusions: Viraph's improved speed for measurement has made VGA analysis more accessible for general design researchers and practitioners. Further this paper shows that the added feature of measuring the interspatial depth opens a new perspective for enhancing traditional space syntax analysis.