Uh...it's simple...you have city boundaries...the expansion could be something off the map...a suburb, neighboring city, whatever...it is possible...I don't know...
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )