Overt Control (Xv) expresses the visual ‘linking’ dominance of any location; the options each space offers for its immediate neighbours as a junction, or where movement may provide access to multiple restricted visual fields. As such, it is similar to Control (Hillier & Hanson, 1984).

Overt Control increases as an isovist encompasses regions that generate smaller, more isolated isovists than itself; i.e. when a location can ‘see’ regions of space that in turn ‘see’ relatively less, more separated space than it. A prime example of a control location would be the centre of Bentham’s panopticon, surrounded by cells.

To determine control, the Isovist_App generates isovists at stochastically selected locations in the sample region. It then records the sum of the reciprocal of their areas at any point ‘V’ that falls within each isovist generated. The result is divided by the number of isovists generated overall to give a mean value. The resulting value is absolute, expressed as control per scalar area unit (as defined by the user).

In notation form the calculation for control is expressed as:

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