In conducting a cumulative viewshed analysis in the Ilave River valley in the Lake Titicaca Basin (Tripcevich 2001), the maximum view distance was defined as 5 km because a principal goal was to model the observability of camelids (wild or domesticated) and other people traveling in the Ilave valley. It was estimated that a distance of 5 km was the approximate distance that such objects could be seen, with a consideration for the great deal of variability in such situations, including:

- the visual acuity of the observer

- atmospheric conditions

- the amount of contrast between the target and the background

- whether the target was in motion.

Similar criteria exist in the Upper Colca viewshed study, however in this case a 10 km maximum radius was selected for this situation. The rational for doubling the maximum radius from 5 to 10 km was as follows. The goal here is to model ancient visibility, but also environmental exposure. In the much higher relief terrain of the Upper Colca area, observation distances are potentially much greater, and exposure is similarly greater. In order to avoid artificially limiting the amount of view / airspace adjacent to high visibility sites, a 10 km buffer was issued to the RADIUS2 variable for all 5000 random points. Also, a OFFSETB (target) height rather than OFFSETA (viewer) height was raised to 1.5m to simulate the assumed eye level of an Andean adult because the reciprocal viewshed was being calculated in this process.