UIUC has a Gangland Map on the UIUC Library website that was done in 1931 and shows the various gangs involved in the famous gang wars, their respective territories. More about the library's online offerings after the Jump.
The UIUC site contains a large array of maps, mostly historical and with detailed descriptions, very well suited for searching. For a list of maps available try the search term maps in the library search engine.
It appears that MrSID versions were or will be available of some of the offerings, although when I tried to access them, the web server gave a "Page Not Found" error. Hopefully soon.