Viewsheds

Viewsheds are the areas of terrain that are visible from one or more observation points, given terrain data such as a digital elevation model and, often, the observer’s height. They are used to assess landscape visibility for planning, design, and management purposes across fields such as land use, transportation, and natural-resource development.

Computing a viewshed typically involves line-of-sight analysis on a three-dimensional representation of the landscape. The observer’s location and height above ground are specified, and for each cell in the terrain grid the algorithm determines whether any terrain intervenes along the line of sight. Outputs are usually maps showing visible versus nonvisible areas, sometimes accompanied by measures of visibility confidence or distance. Many Geographic Information System (GIS) tools support single-point, multi-point, or relocating observers, as well as cumulative or sum viewsheds that aggregate visibility from several locations.

Viewsheds can be categorized as simple point-based viewsheds, line-of-sight viewsheds along a path, or cumulative viewsheds that count how often a cell is visible from a set of observers. They may also be generated for moving observers, producing time- or path-based visibility results. Outputs are commonly used to quantify landscape openness, assess scenic quality, and evaluate suitability for siting facilities such as antennas, wind turbines, or solar arrays.

Limitations of viewshed analysis include reliance on terrain data quality and resolution, and the typical omission of non-terrain factors such as vegetation canopy, built structures, atmospheric conditions, or seasonal variability. Observer height, time of day, and data accuracy all influence results. Despite these limitations, viewsheds remain a fundamental tool in planning and risk assessment.