Viewshed Analysis

Viewshed analysis, a form of visibility analysis that identifies visibility between points in a landscape, emerged as a geographic field several decades ago. Recent advances in software and computing power enabled viewshed analysis to become a common form of geographical analysis, and it is now a standard tool in many geographic [Page 3017]information systems, enabling viewshed analysis to be used in a range of fields. The following entry discusses the techniques used to calculate and analyze viewsheds as well as the applications of viewshed analysis.

Figure 1 Sample viewshed

Source: Author.

Viewshed analysis is typically conducted as a raster-based operation in a GIS. It begins with the calculation of a viewshed, a two-dimensional (2D) projection of a view, using one of many algorithms (see DeFloriani & Magillo, 2003). The viewshed procedure identifies landscape areas that are visible from a given location based on elevations from a digital terrain model (e.g., digital elevation model, triangulated irregular network) and accounting for that location's height and position, the view angle, and, frequently, a viewer height offset or maximum-view radius. Locations that connect to the observation location by a line-of-sight are identified as visible and part of the observation location's viewshed, while all other locations are not. The resulting viewshed thus approximates the view from a given location (Figure 1).

The structure of calculated viewsheds is analyzed using metrics that quantify viewshed characteristics. Numerous viewshed metrics exist and include measures of size, complexity, and relief as well as the visual prominence of landscape features of interest. Viewsheds for an observation point may be calculated under different land use scenarios and their metrics compared to assess [Page 3018]the impacts of proposed land use changes on scenic quality. Viewsheds may also be visualized and compared in three dimensions using 3D modeling techniques.

A variety of fields use viewshed analysis. In planning, it is often used to identify the potential scenic impact of proposed landscape changes (e.g., van der Horst, 2006). Viewshed analysis is also used to identify the economic values of different view types using economic valuation techniques (e.g., Bastian, Reiners, Blasko, McLeod, & Germino, 2002). Additionally, archaeologists employ viewshed analysis to reconstruct past landscapes or cultural interactions (e.g., Lake & Woodman, 2003).