But I said to keep population equal. Take two million people, and put a million in a city as dense as Manhattan (74,780.7/sq mi), and the other million in a city as dense as Jacksonville, Florida (1,270.73/sq mi). So New Manhattan would be 13 square miles, and New Jacksonville would be 787 square miles. It seems obvious to me that most things in New Manhattan would be more efficient and cheaper. You'd need fewer police officers to have the same patrol density. You'd have a couple larger fire stations instead of numerous smaller ones. You'd have far less utility and road infrastructure to maintain. Everyone would spend less time traveling places, because everything's so close together, and fewer people would feel like they had to purchase a personal vehicle, which means fewer and smaller parking lots to pave. You have to make other tradeoffs for this bonus, of course, and many find those tradeoffs unacceptable, which is fine. But it seems like efficiency is density's greatest strength, to me.