How do you get out of maps in forge in Halo 3?

[lalakers2o3]

I played a lot of forged maps and game variants on Halo 3 that are outside the map boundaries. I dont know how my friends do it.. Does any one know how to do it?? My friend said something about "overloading" the map.. whats that?
Can someone show me how to do it step by step and does it work on any map?
And im not talking about how to get out in theater mode. Im talking about getting out in forge and then playing outside of it
Thanks