Where is Metropolis suppose to be?

If Gotham is New York City, Where is Metropolis suppose to be? The Smallville series makes it sound like it is not that far from Smallville(within casual driving distance). However in the Lois & Clark series Clark makes mention of flying over Cleveland on his way from Metropolis to Smallville. And then the old Christopher Reeve movies at least suggest that it is somewhere around Niagara Falls. I was never really into the comics so I was wondering if somewhere along the lines its relative location was better described?