Drift-isovist is defined as the distance in metres between the location from which the isovist is generated and the centre of gravity of the isovist. It will tend to a minimum value in the centres of spaces and along the centre-lines of roads.
Drift -isovist
Sources
Dalton, C. R. & Dalton, N. (2001), OmniVista: An Application for Isovist Field and Path Analysis, In: Proceedings of 3rd International Space Syntax Symposium Atlanta, 25.1-10. pp.25.9