Officially not a lot:
https://ashesofcreation.wiki/Template:Mini_map
Hopefully we will see party members disapear from the mini map under certain circunstances, like under heavy fog, anywhere with very limited visibility, when they go into caves or to other areas.
By me, we would only be able to see people in the map if they are within a certain range and not inside something like a bunker. If the party is running in a labyrinth, why should the party know where everybody is? In other games we can see where everybody is at all times and we just rush to them using our mounts, people don't even have chat sometimes at all, there's public parties which people don't talk at all and they don't bond, it is pretty tasteless.
Let me share stuff from the hidden world of pvp, knowing where everybody is, including all guild members, is a resource which was used in the past to kill guild members by throwing alts at them. It was also used for spying quite a lot too, you just gotta add an alt in your enemye's guild.