Can anyone explain how online works in these games?

How does the online aspect work? Like the structures I see and the notifications about other players I see…surely not all global players see the “same” map right? Are all global players randomly assigned to a smaller cohort, and that’s who share “a map”?

If everyone is seeing the same content/structures, etc, why isn’t the map LOADED with them? That’s why I assumed there were small cohorts.