Viewshed Analysis

Viewshed analysis is a GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... technique that calculates the areas of a terrain surface that are visible from one or more specified observation points, producing a binary or cumulative visibility map. By tracing sight lines from observer locations across a digital elevation model, viewshed analysis identifies which cells are visible and which are occluded by intervening terrain, providing essential information for applications where line-of-sight visibility drives decisions.

Viewshed analysis operates by projecting lines of sight from an observer point (or set of points) to every cell in the surrounding DEM. For each target cell, the algorithm checks whether the line of sightLine of SightLine of sight analysis determines whether a direct, unobstructed visual connection exists between two points across a... is blocked by any intervening terrain cells. If no cell along the sight line has an elevation that exceeds the line-of-sight angle, the target cell is classified as visible; otherwise it is classified as not visible. Observer parameters include the observer's height above ground, the target height above ground, the maximum viewing distance (radius), and optional horizontal and vertical angle constraints that limit the analysis to a specific viewing cone. The result is a raster surface where each cell indicates whether it is visible from the observer, or in multi-observer analyses, how many observer points can see each cell.

Viewshed analysis is applied across numerous fields where visibility is a critical factor. Telecommunications planning uses viewshed analysis to determine cell tower placement that maximizes signal coverage across terrain, minimizing dead zones while reducing the number of required towers. Military and security operations evaluate observation post locations, defensive positions, and surveillance coverage based on terrain visibility. Landscape architecture and urban planningUrban PlanningUrban Planning is the systematic process of designing and managing the development of cities and communities. It inte... assess the visual impact of proposed structures, wind turbines, or transmission lines on scenic landscapes and protected viewpoints. Real estate valuation considers viewshed analysis results, as properties with unobstructed scenic views command premium prices. Conservation management evaluates the visual intrusion of development proposals on national parks and heritage sites. Wildfire lookout placement optimizes the network of observation stations to maximize terrain surveillance coverage.

Viewshed analysis provides objective, quantitative assessment of visibility that replaces subjective field observation. It can evaluate visibility from locations that are difficult or impossible to physically visit. Multi-observer viewshed analysis enables optimal placement of facilities to maximize or minimize visibility across a landscape. The technique integrates readily with other GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... analyses in multi-criteria evaluation frameworks.

Viewshed accuracy depends on DEM resolution and quality; coarse elevation data may miss terrain features that block or enable visibility. Standard viewshed analysis considers only terrain, ignoring vegetation, buildings, and atmospheric conditions that significantly affect real-world visibility. The binary visible/not-visible classification does not account for distance-based degradation of visual perception. Large study areas with high-resolution DEMs require substantial computational resources, as the algorithm must evaluate visibility for every cell.

DSM-based viewshed analysis incorporating vegetation and building heights produces more realistic visibility models. Probabilistic viewshed approaches account for uncertainty in observer and target heights and atmospheric conditions. GPU-accelerated viewshed computation enables real-time analysis for interactive siting applications. Integration with 3D city models extends viewshed analysis into urban environments with complex building geometries.