This is work that was started for the US Army Topographic Engineering Center, formerly the Engineer Topographic Labs, at Ft. The general problem is to defend an area against enemy air attack by planes or Scuds.
Some terrain is more valuable and critical than other terrain.
Specifically we wish to site these defenses in the best places. There are mobility restrictions, e.g., we can't drive through a swamp, but perhaps can use a helicopter to lift something over it. First, determining the terrain or airspace visible from a proposed site, and, second, determining the sites with most combined visibility, are major problems. Mountain is the single best point for viewing the most terrain. Currently the siting is done manually, except for a program that runs 360 rays out from a given site to calculate approximate visibility.