Gotham City Mapped

Batman co-creator Bill Finger first named Gotham in 1940 for Batman #4. However, the city was not mapped until 1998, when a plot involving a catastrophic earthquake required a map. Artist and illustrator Elliot R. Brown was hired for the task.

The city has always had a resemblance to New York but, according to Finger "We didn’t call it New York because we wanted anybody in any city to identify with it." With no formal training in cartography, Brown was tasked with creating a city that had all the necessary diverse elements.

"The DC Comics editors made it clear that Gotham City was an idealized version of Manhattan. Like most comic book constructs, it had to do a lot of things. It needed sophistication and a seamy side. A business district and fine residences. Entertainment, meat packing, garment district, docks and their dockside business. In short all of Manhattan and Brooklyn stuffed into a … well, a nice page layout." - Brown

Early sketches of his map can be seen on his website, including this one.

The city needed to be an island so that federal agents could seal it off from the mainland by dynamiting the bridges and tunnels. In addition to the New York elements, he also added some "Chicago-like" bridges in the middle of town, to "add some story potential."

Here is one version of the final product as it appeared in the comics circa 1999, via Smithsonian.

So where is Gotham City? It is often considered to be on the east coast of the United States but it's an open question due to some contradictory descriptions of it's location. From io9's Is Gotham City Really in New Jersey?

Gotham also has been hit by earthquakes (1999's No Man's Land...), sits in the Central Time Zone (Man-Bat #3), and was a cowboy town in the 1800s (2011's All-Star Western).

The Batman wikia has a modified google map placing Gotham in Great Bay, just north of Brigantine (and Atlantic City), New Jersey.

The io9 page shows this image from a 1978 comic also placing Gotham in South Jersey but on the Delaware Bay, across from Metropolis (Metropolis, Delaware?)

That's a lot of action for an area mainly populated by horseshoe crabs.