How can I get the grid to line up with the walls?

[Pyroguy]

Assuming I'm using the default map, how do I get the grid to line up with the walls? So that the walls are directly over grid lines.

[Z-Man]

In the ingame menu, in "Change Game/Game Setup", you set the arena size to -4, -2, 0 or a positive even number. For network games on dedicated servers, you set SIZE_FACTOR and SP_SIZE_FACTOR to those values, but be aware that this also assumes default client textures and default client settings.