Visual Space Index

The need exists for a simple index to characterize the amount of visual space about an observer. This is the open space between the observer, in any direction, up to the point of visual blockage by vegetation structures or topography. The visual space index (VSI) is proposed to help meet this need. It is defined as the percentage of a horizontal circle, of specified radius, about an observer that is clear and unblocked by intervening objects. The circle lies in a plane, 4·5 feet above the ground. Information on the direction of the visual blockage from the point is provided by a visual blockage diagram. Several examples of the computation of the visual space index surface and the generation of visual blockage diagrams for forested sites are presented. The effects of heterogeneous distributions of vegetation and shrubs on VSI are also presented as is a discussion of the field measurement of the index and its applications to various areas.