people can be walking around 'in a building' and be able to see the relative location of each of their people in their groups.
Off the top of my head I can't think of any way to do this, GPS is not accurate enough and won't work inside anyway. With any form of radio you either need several "master" nodes that can get direction from transmitters and then triangulate, or each person's gadget has to be able to determine direction and signal strength of it's neighbours. And given that the signal strength would be a bad indication of distance due to walls etc I don't see that working.
The last technique is actually used quite well by those tiny swarm robots, but that's in in a very controlled environment.
I suppose each person could have an INS and that data could be transmitted to all other units. How much that would creep over time without a reference I don't know.
Rob