The viewshed operation is integral to a number of modern geographic information systems. From a digital elevation model of an area, it derives a new coverage which shows those areas which are visible from one or more locations, and which is coded as a binary image: 1 indicating those areas which are visible, and 0 those which are not. For various reasons this representation has been shown to be insufficient and it has been suggested elsewhere that the probable viewshed is a more realistic alternative. In this paper the use of the probable viewshed in planning visible areas is explored. This involves a discussion of combining probable viewsheds by union, intersection, and weighted average. The data products thus derived are examined and it is shown that the analysis of probable viewsheds gives much more information about the nature of the viewable area, which in turn enables a more thorough approach to planning the use of viewable areas.