Visibility graph analysis investigates the properties of a visibility graph derived from a spatial environment. The VGA can be applied to two levels, eye level for what people can see, and knee level for how people can move which is critical to understand spatial layouts. See: visibility graph.
VGA (visibility graph analysis)
Turner, A., Doxa, M., O’Sullivan, D., and Penn, A. (2001) From Isovists to Visibility Graphs: A Methodology for the Analysis of Arcthiectural Space. Environment and Planning B: vol 28, 103-121. pp.108-109