And I just found a reference to a map - According to the IMDB record for Superman Returns:
Lex's computer map on the boat shows Metropolis in the real-world location of Bayonne, New Jersey.
According to Wikipedia:
As of the 2010 United States Census, there were 63,024 people, 25,237 households, and 16,051 families residing in the city.
So about a hundredth the size of Metropolis!
I really need to watch the movie again and check the coordinates in the fax that Lois sends to the Daily Planet - assuming a top speed for the ship of say 30 knots, it couldn't have been more than 60 miles or so from Metropolis.
