Viewshed Analysis


Viewshed analysis is a spatial analysis method in Geographic Information System (GIS) which is used to determine the visibility of a particular object or an area. It takes into account various factors such as topography, the presence of objects blocking the view, and viewer height to create a map or a model, showing the region that is visible from a specific location or a sequence of locations. The resulting visibility area is known as the viewshed.

What is Viewshed Analysis?

Viewshed analysis is a digital tool used to model and analyze the visual impact of topographical features, landscapes, and built environments. It's a key function in many GIS software and has extensive applications in various fields such as environmental management, archaeology, urban planning, defense strategy, and more.

In the process of a viewshed analysis, the visibility from a given observer's point or points (known as viewpoint or viewing point) to every other point in a landscape is determined. This is done by comparing the angle of the observer's line of sight to the angle of the topographic surface at each point. If the line of sight is above the surface angle, the point is considered visible; otherwise, it is invisible.

The outcome of a Viewshed Analysis is a binary raster layer with cells coded as either visible (usually represented by 1) or not visible (represented by 0) from the selected viewpoint(s).


What are the applications of Viewshed Analysis?

Viewshed analysis is frequently used in environmental planning to examine the possible impact of a new development, in military strategy to evaluate the visibility of strategic areas, in landscape design to optimize scenic views, and in ecotourism planning to retain the aesthetic value of an area.

How does the height of the observer affect a Viewshed Analysis?

An observer height significantly influences the result of the viewshed analysis. A higher viewpoint will generally result in a larger visible area, while a lower viewpoint tends to limit the visibility.

What factors can influence the result of a Viewshed Analysis?

Factors influencing a viewshed include the local topography, the presence of obstructing elements such as trees or buildings, the observer's height, and the analysis settings, such as horizontal or vertical angle limits, and the curvature and refraction of the Earth.

Is Viewshed Analysis only applicable to land-based studies?

No, Viewshed Analysis is not limited to land-based studies. It is applicable to sea and air views as well. For instance, it can be used for coastal management, offshore wind farm visualization, flight path planning, and more.

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