A viewshed map is used to illustrate what aspect of a landscape?

A viewshed map is employed primarily to represent the locations visible from a specific viewpoint. This type of analysis is crucial in fields such as landscape architecture, urban planning, and environmental studies, as it helps to visualize and understand how various landscapes are perceived from designated positions. The viewshed analysis takes into consideration factors such as terrain elevation, obstacles like buildings and trees, and the line of sight.

This mapping technique is particularly valuable for assessing visual impacts of proposed developments, planning scenic routes, and protecting viewsheds in conservation areas. The information gleaned from a viewshed map can guide decision makers in ensuring that development and land use plans respect the visual character of an area and the visual interests of the public.

The other options, while related to aspects of landscape analysis, do not accurately describe the primary purpose of a viewshed map. Elevation changes, water drainage patterns, and areas of urban development can be illustrated using other types of mapping techniques and analyses, but they do not define the specific function of a viewshed map.