In order to restrict AI movement you need to reduce the character navigational mesh to show only the areas you want your AI to travel. You can view the navigational mesh by selecting "View Navigation Mesh: Characters" in the editor option. Areas in the bluish purple represent surfaces the AI can navigate.
Unfortunately, there is no way to limit the navigational mesh outside of editing the terrain or objects to fence in the navigational mesh area. You can edit the terrain by making un-scale-able mountains or cliffs. You can also create ledges, grapple points, or rivers (like a moot) around the area you wish AI to be trapped within (these type of terrain edits will still be navigational by the player, but not by the AI).
You can also, increase the probability of AI being in specific locations by editing animation points which AI will randomly occupy for the duration you set. Animals and characters have different control point options. There is more information about this on page 4 of the stickyed "Far Cry 4 Map Editor Thread", and on my old thread titled, "Single Player Map Editor First Impressions."