The admin wrote that all the parties in the 1st layer will be where the party leader is. So if you need someone from your friends nearby, you just throw a party and imagine him spoiling into your layer.
He wrote that they would make a limit of 500 people for cities, and everything above that would fall into a new mirror image of this city. There is a limit of 200 people in reno quest locations. Everyone who is in the same party gets into the same layer
