Viewshed analysis has been included in CRM in recent years, and is made very easy through GIS technology. In CRM, a project may prove to have adverse impacts on a National Register Eligible or listed culutral resource if it falls within the resource's viewshed. In other words, the visibility of a project may adversely effect a cultural resource's integrity of setting, feeling, design, and/or association under the applicable legislation and guidelines. Viewshed analysis is not limited to cultural resources, either. Viewshed issues are also important when a project is located within view of a national scenic area, scenic byway, or national park.
Viewshed Analysis in GIS employs terrain surfaces, such as Digital Elevation Models (DEM), LiDAR, etc. The user selects a "point of origin" (a project site or scenic area, for example), runs the analysis, and then receives an output that shows what areas are visible from the point of origin (see the first graphic below). Depending on the quality of the terrain surface used, results can be quite dependable. However, many datasets do not account for the height of vegetation or built-environment structures; these limitations can effect output.
Another effective way to conduct a viewshed study for a cultural resource project is through a Line-of-Sight Analysis. This method is very useful when you know both your project location and the location of nearby Eligible cultural resources. The analysis works in much the same way as the general viewshed analysis, but instead of a generalized raster-like output, the user draws a line from point A to point B (say, from an Eligible cultural resource to a project area), runs the analysis, and receives their input line colored in two tones: one for visible portions of the sight line, and the other for non-visible portions of the sight line. The same limitations exist for this type of analysis as they do for the generalized viewshed analysis. The second graphic below illustrates this type of analysis.