I'm making an online game with a friend, and we are stuck in a dillema.
Each player will have his residence in an X/Y coordinate system (or perhaps even a Z one will come in place - as another city).

I believe a query will be very time consuming if it will be done on two or three indices. I was thinking that giving the "map" a default width (i'm going with a square map) could help me in solving this, by giving each position a Y*wid+X index value.

However, if the game extends, and I will need to create more space, it will require everyone to log off and a specially designed script to update all indices (I want positions with + and -, the rought center beeing 0,0). I don't know if this is a very good idea.

What would you suggest?