Outposts: I just found out what exactly the outposts are. In Far Cry 5 it was more obvious, well to me anyways. Outposts that you can capture will have the red flag.
An Analysis of Far Cry 5: Outposts
Far Cry 5 Gameplay - Liberating Outposts (Stealth) - YouTube
Far Cry 5 All Outpost Locations
Far Cry 5 Outpost Guide - All 20 Outpost Locations - Gamepur