Heights and locations of artificial structures in viewshed calculation: How close is close enough?

Viewshed calculation can play an important role in urban and natural resource planning. However, difficulties exist in incorporating built structures in viewshed computation. These features are rarely reflected in available elevation maps and adding them can be complicated as their locations, shapes, and heights are often uncertain. This study examined the impact of generalizing building locations and heights on viewshed properties. We used a geographic information system and high resolution data to assess how viewsheds, generated with actual building footprints and heights, differ from viewsheds generated from generalized building locations and uniform heights. We measured differences among viewsheds created with different approaches in terms of area and landscape complexity. Viewsheds generated using uniform heights and actual footprints differed significantly from the most accurate viewsheds in their areal extents and in the areas of some land use classes. Viewsheds produced using estimated locations combined with both realistic and uniform heights differed significantly from viewsheds created with accurate data in their areal extents and areas most land use types. Viewsheds produced using estimated locations also differed significantly from more accurate viewsheds in both complexity metrics assessed. Viewsheds produced using accurate locations and uniform heights differed significantly in one complexity metric, richness, but not in a second, diversity. Therefore, it may be feasible to generalize building heights when diversity and the areas of some specific land use classes are central to viewshed analysis, but generalizing building locations is less advisable. When viewshed areal extents are critical, location or height generalization may be ill-advised.