From Isovists to Visibility Graphs: A Methodology for the Analysis of Architectural Space

Abstract

The concept of an isovist has had a long history in both architecture and geography, as well as mathematics. Tandy (1967) appears to have been the originator of the term isovist'. He presents isovists as a method of``taking away from the [architectural or landscape] site a permanent record of what would otherwise be dependent on either memory or upon an unwieldy number of annotated photographs'' (page 9). The same idea has a similarly long history in the guise of the`viewshed' in the field of landscape architecture and planning (Amidon and Elsner, 1968; Lynch, 1976) and in terms of intervisibility' in computer topographic models (Gallagher, 1972). The appeal of the concept is that isovists are an intuitively attractive way of thinking about a spatial environment, because they provide a description of the spacè from inside', from the point of view of individuals, as they perceive it, interact with it, and move through it. As such, isovists have particular relevance to architectural analysis. Benedikt (1979) introduced a set of analytic measurements of isovist properties to be applied to achieve quantitative descriptions of spatial environments. Benedikt starts by considering the volume visible from a location and then simplifies this representation by taking a horizontal slice through the`isovist polyhedron'. The resulting`isovists' are always single polygons without holes, as shown in figure 1 (see over). Consequently, Benedikt considers geometric properties of isovists, such as area and perimeter. Thus he begins to quantify space, or what our perception of space might be, and the potential for its use. Benedikt notes that, in order to quantify a whole configuration, more than a single isovist is required and he suggests that the way in which we experience a space, and how we use it, is related to the interplay of isovists. This leads

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