White Castle is an outpost - this could mean that it is a level 1 city, or something less than level 1, or it could simply be a term used for a city on the edge of a side's territory, far from the capital.
Real World References
White Castle is a fast food chain existing primarily in the North Eastern United States. It is famous for its "sliders," (small hamburgers). Since slang for hoodlums includes "greasers", and the burgers are cooked in grease, it is consistent that a gang-based pun for the Transylvitio side would have a city named after a fast food place where hoodlums traditionally hang out.