Neurophysiological data and behavioral theory suggest that enclosure is a very important property of the environment. One technique for measuring enclosure is the mathematical construct of an isovist. An isovist is the set of points visible from a location. This paper reports analyses of 15 521 environments, ranging from cabin configurations in space stations to site plans for cities. Although results have been reported for twenty-five variables, it appears that only a few would be sufficient to distinguish between isovists. The most plausible variables are horizontal size and concavity. Judged <?tlsb=0.015w>enclosure was most strongly related to horizontal size, but it was also correlated with the variation in distance from the observation point to the isovist boundary, with boundary predictability, and with concavity. Numerical estimates of effect sizes are reported to assist in the efficient planning of future research.
