Batman v Superman: Dawn of Justice director Zack Snyder during the San Diego Comic Con panel this year, spoke on Gotham and Metropolis being separated by a Bay, comparing both cities to that of Oakland and San Fransisco, but in his comment he wasn’t sure if the idea of Gotham and Metropolis being right next to each other was canon to the comics:
“The big rule that we broke is that we put Gotham and Metropolis right next to each other, donno if appear that way ever, maybe somewhere. Possibly it’s been, you know if you dig deep enough you can find a justification for about everything. But it makes sense to us and our story, that they were sister-sister cities across a big bay. It’s like Oakland and San Fransisco, kind of vibe.”
Ben Affleck (Batman) also spoke on it during the panel, also confirming that the cities would have a body of water separating them, as people would have to take the ferry from Gotham to Metropolis:
There’s this interesting idea of Metropolis being this successful, wealthy city and Gotham being where downtrodden people live. Gotham people take the ferry to Metropolis, and there’s this idea of wealth and power, power engenders fear, which made it feel real and smart.”
That being said, we can confirm that the idea of Gotham and Metropolis being separated by a Bay isn’t new, that Zack and company did not break any rules with it by using it in Batman v Superman: Dawn of Justice or in general in the DC Extended Universe.
In fact in 1978 in the Sunday newspaper the comic “World’s Greatest Super Heroes” featured Gotham being located in Southern New Jersey, with Metropolis being right across the Bay in Delaware:
Then again in 1979 in “World’s Finest” #259 had Gotham and Metropolis as neighboring cities, as the story goes in the issue, people of Gotham try to attempt a mass immigration into Metropolis using the Metro-Narrows Bridge:
The same Metro-Narrows Bridge seen in a 1981 issue of “New Adventures of Superboy” #22, which also shows Gotham and Metropolis being right across from each other, with Smallville not that far in the distance either:
In 1990 Mayfair Games published The Atlas of the DC Universe as a supplement to its DC Heroes role-playing game, the atlas had a complete guide to the cities in the DC Comics Universe and their placements, which you guessed it, had Gotham and Metropolis right across from each other with a Bay in between them:
We believe there’s most likely more examples of this throughout the DC Comics run between the two cities, so if anyone you know dares to take issue with the idea of Gotham and Metropolis being right next to each other in Batman v Superman: Dawn of Justice, think of this article and the four examples above.