A single isovist is the volume of space visible from a given point in space, together with a specification of the location of that point. It is a geometric concept coined by Clifford Tandy in 1967 and further refined by the architect Michael Benedikt. Isovists are naturally three-dimensional, but they may also be studied in two dimensions: either in horizontal section ("plan") or in other vertical sections through the three-dimensional isovist. Every point in physical space has an isovist associated with it.