A viewshed is a spatial analysis technique used in GIS to determine all locations visible from a specific observer point across a defined terrain or landscape. Leveraging digital elevation models (DEMs) and raster-based geospatial data, GIS platforms calculate line-of-sight relationships between an observer and surrounding geography, generating visual output that distinguishes visible areas from obstructed ones.

The analysis works by evaluating elevation values across a raster dataset, accounting for terrain features, observer height, target height, and maximum viewing distance. Advanced GIS workflows can incorporate additional variables such as atmospheric refraction, surface curvature, and man-made structures to increase analytical precision.

Viewshed analysis delivers measurable practical value across multiple disciplines. In telecommunications, it optimizes antenna and cell tower placement by identifying maximum signal coverage areas. Military and defense applications use it for strategic positioning and surveillance planning. Urban planners rely on viewshed mapping to assess visual impact from proposed developments, while conservationists apply it to protect scenic corridors and evaluate habitat connectivity. As a foundational geospatial analysis tool, viewshed functionality remains essential within leading GIS platforms including ArcGIS and QGIS.