Co-Visibility (Rv) accounts for the average area visible within one visual step from a location (Psarra and McElhinney, 2014). In isovist terms, co-visibility represents the mean area of isovist generated from all points encompassed by the isovist at point ‘V’; or, more simply, the mean area of all isovists that point ‘V’ is seen within.

Co-visibility indicates the degree to which an individual at a location is engaged in a reciprocity of ’seeing and being seen’. A location that is high in co-visibility both sees, and is seen alongside, a large number of other locations. A location that is low in co-visibility both sees, and is seen with, fewer other locations.

To calculate Co-visibility, the isovist_app generates isovists at stochastically selected locations in the sample region. It then records the sum of their areas at any point ‘V’ that occurs within them. The result is divided by the number of isovists generated overall to give a mean value. The resulting value is absolute, expressed as scalar area units (as defined by the user).

Where ‘Ai’ is the area of any isovist that point V falls within; ‘Av’ the area at point V; and ‘n’ the total number of isovist samples.