Constructing an influence map requires configuration parameters as well as a navigation mesh on which we can base the influence map. Instead of analyzing all geometry in the sandbox, an optimization is done by constructing grid cells along the navigation mesh itself. As all walkable areas are represented by the navigation mesh, the influence map will be able to store spatial data for all regions that agents can path to.

A navigation mesh used to construct the influence map

While information about all possible areas might be useful for certain tactical analysis, in practice, the additional memory and performance constraints are a higher priority.