That's perfect, thanks. In hindsight it does make sense for them to be up there with the navmesh and portal type things. ^^
Yeah after examining the NV Wasteland cells I absolutely agree with their placement and rationale. I think their presence threw alot of people off-guard because Fallout3 has none of these in the wasteland, and their addition represents a different style of level design between the two companies. Obsidian setup the wasteland such that they wanted/needed the player to approach areas from certain directions to ensure that the story flows correctly. Black Mountain is a good example;
Spoiler
If we were able to approach it from any direction, we might never meet Neil and would miss that entire interaction regarding Black Mountain and his troubles with Tabetha.
Whereas Fallout3 handles story elements differently, the walls definitely "enable" the story to proceed correctly for all/most players in New Vegas