Gotham City is the home of Batman and his allies and enemies. While it's location varies from writer to writer, most put Gotham on the Eastern Sea Board, usually within driving distance to Metropolis. But every incarnation depicts Gotham as a city with one of the largest crime rates in the world. The city is plagued by violent crime from mobsters, street gangs, to even supervillains. This crime rate is what took Bruce Wayne's parents from him, and he vowed to spend the rest of his life ridding Gotham if it's crime wave.