Why was Gotham City changed from a mostly fictional city to New York City in the Nolan trilogy?

Question

In Batman Begins, Gotham City has a futuristic/fictional and run down look: think of Oldtown, the trains built by the Wayne Corporation etc.

In The Dark Knight Rises, Gotham City looks like plain old real world New York City — we don't see the trains anymore. Oldtown is just a standard poor neighborhood. Lots of the locations used in the movie are easily identified as real world NYC locations: the stock exchange or East River bridges for example.

My question is: Why did Nolan change Gotham city from a shady fictional more cartoon-like town to plain old NYC?

Edit: The examples from Batman Begins and The Dark Knight Rises were just for illustration; I didn't intend to limit the question to those two movies.

Edit 2: I specifically want to know why Gotham City was changed from a cartoon-like city in Begins to an almost real-world NYC in The Dark Knight Rises (via not so cartoon-like but not yet real-world like Chicago in The Dark Knight Rises). Why it's NYC or Chicago is not so important for me. But why, e.g., were the trains which featured prominently in Begins gone in The Dark Knight Rises? There was only a very short in-universe time-span between the events of the two movies, yet Gotham changed drastically.

Answer 1

Thematically, it just makes sense.

When the series begins, Gotham City is incredibly corrupt and crime is rampant. Wayne Enterprises is run by a greedy CEO. Gotham City lives in fear, and the League of Shadows has deemed it so far gone, that it must be completely destroyed.

Then Batman arrives and starts protecting the city at the street level. Harvey Dent arrives and starts his war on crime on the more official level. Now instead of every citizen being a victim, you have many standing up to do the right thing. Bruce Wayne has turned Wayne Enterprises around. Gotham has started rebuilding itself from the ground up.

By the time Bane shows up, Gotham has made a lot of headway. It's the sort of big, successful city or metropolis (not to be confused with the city) that one typically identifies with modern cities such as New York.

You also have the whole dark-to-light theme of the series. Gotham starts a dark, dangerous place and becomes a bright and shiny place full of hope. This is expressed through the story itself, the color/lighting scheme and even the very design of Gotham City.

Answer 2

Basically everyone has always known "Gotham" was supposed to be NYC. There are old pre WW2 radio broadcast and movie reels where NYC is literally refered to as Gotham almost the same way as Hollywood was referenced as "Tinsel Town." So kind of an open secret though its not as common in the present day.

This might in part be due to the fact that NYC was set as Metropolis in the Christopher Reeves Superman movies, even though those same old radio and movie references refered to Chicago as Metropolis. If you look at how they were originally depicted Metropolis was a huge city on the plains of the Midwest surrounded by corn fields. Does that sound like NYC or Chicago? Meanwhile Gotham had everything from the same architecture to similar geography as NYC.

So everyone just pretty much knew... I wouldn't be that surprised if Nolan specifically set it in what's obviously NYC exactly to reassert that NYC is Gotham, not Metropolis.