Very good explanation how existing maps can be modified, not all applies to Enemy-Territory as its for Jedi Academy.
Ever since I made the first JA map mods and showed Boba the technique, one of the most common questions we've been asked is how to do it. Anyway, I hope you all enjoy this. :) - Jahandar
Found a nice tool for Neverball, the maps for that game are aswell created with .*Radiant, this tool can create all sorts of curves, slopes, hills, spirals.. and