*Choice* (Zv) expresses the how likely it is for any location to be seen on all shortest routes from all spaces to all other spaces (Hillier, 1987). In graph terminology, it relates to ‘Betweeness Centrality’ (Freeman, 1977). In isovist terminology, choice represents how often a location falls within isovists generated by random walks through space.

To determine choice, the Isovist_App generates all isovists along the shortest path between two points at stochastically selected locations in the sample region. It then records any point ‘V’ that falls within each isovist generated. The resulting ‘score’ at V is divided by the number of isovists generated overall to give a mean value. The result is a relative value between 0 and 1.

In notation form the calculation for choice is expressed as:

*Where ‘Bi’ is either 0 or 1 depending on whether point V falls within a sample isovist chain; and ‘n’ the total number of isovist samples.*