The following are details about the Criminal Organizations in Gotham, within the Earth-27 continuity.
The Gangs of Gotham
The Masterminds are a confederation of criminal elements that collectively rule most of Gotham, having seized up most of the power that was once held by Carmine Falcone and Sal Maroni. The Masterminds are mostly free to run their own operation as they see fit but meet together as needed to work through internal disputes or conduct other business.
Black Mask has the largest slice of Gotham. His gang rules the vast majority of the West Side of Gotham. Black Mask's gang, the False Face Society (aka: False Facers), are headquartered out of the Sionis Steel facility. Their business mainly consists of protection rackets, illegal gambling, and dealing drugs.
Great White Shark has the next largest slice of Gotham, the East Side. People who wrong the Shark tend to end up in the Atlantic.