Exact Locations of raves are usually collected from the map point. The map point is usually a close friend of the rave organiser, and has a collection of slips of paper which hold exact directions to the party. It is usually at the map point that the entry fee (if any) is paid.
Please note that the map point is only used when dealing with illegal warehouse raves, this way the police will have a much more difficult time tracking the location of the venue.