In Batman vs Superman, Metropolis is apparently just across the bay from Gotham City. Has this ever shown up in any of the comics or shows before? And if they've been so close, why hasn't Batman met Superman before? I mean they're so close, they could have met for lunch or something.
Since when was Metropolis just across the bay from Gotham City? Has this ever shown up in any of the comics or shows before?
Distance between Metropolis and Gotham City have changed a lot in comics.
Metropolis is frequently depicted as being within driving distance of Gotham City, home of Batman. This happens, for example, in the three-issue 1990 mini-series of World's Finest Comics by Dave Gibbons, Steve Rude, and Karl Kesel. Like Metropolis, Gotham's location has never been definitively established; however, it is usually treated as also being a major city. The distance between the two cities has varied greatly over the years, ranging from being hundreds of miles apart to Gotham and Metropolis being twin cities on opposite sides of Delaware Bay, with Gotham City in the location of Cape May Point, New Jersey and Metropolis in the location of Lewes, Delaware.
In the TV series Smallville, Linda Lake, a columnist for the Daily Planet, once boasted that she could see Gotham City from her new office.
In Bronze Age stories that depicted Metropolis and Gotham City as twin cities, the Metro-Narrows Bridge was said to be the main route connecting Metropolis to Gotham City.
In The World's Greatest Superheroes newspaper comic strip, a 1978 Sunday strip shows a map of the east coast of the United States; the map places Metropolis in Delaware and Gotham City across Delaware Bay in New Jersey, with the Metro-Narrows Bridge linking the two cities.
A similar map appeared in The New Adventures of Superboy #22 (October 1981), with Smallville shown within driving distance of both cities (in post-Crisis comics, Smallville was officially relocated to Kansas). 1990's The Atlas of the DC Universe also places Metropolis in Delaware and Gotham City in New Jersey. - Wikipedia
So Zack Snyder also did what had already been done many times in the comics and other shows, changing the location of Metropolis and Gotham City to the requirement of story.
If you have to show the impact of Man of Steel film's destruction in Gotham city, then this is the best solution for placing them next to each other.
During the filming of Man of Steel, there was nothing fixed for the future films, so they never mentioned where is Gotham City.
Why hasn't Batman met Superman before?
In-Universe: They didn't meet each other in the film because Clark was in Smallville and he didn't have much interaction with big cities before, he hadn't even heard about Bruce Wayne before. But in comics and Cartoon shows they did meet each other a lot, sometimes knowing their secret identity and sometimes not, but most of the time they are driving distance away, not this near.
Out-of-Universe: As mentioned before during Man of Steel shooting future of this films were not set, that's why they didn't mentioned the location of Gotham city.