The server map files are not the same thing as the client map files. The server map files are basically all of the 3D data for each zone and structures inside them. Without the server map files, the server doesn't know the layout of the zone. There is nothing to restrict Line of Sight, and nothing to tell the server when an NPC is walking over a hill if you don't have maps installed. So, you will have NPCs that jump a lot when they path through bumpy terrain and you will be able to cast through walls. NPCs will also be able to aggro through walls as there is nothing telling the server there is a wall there, so it just sees you are within range and attacks.
|