Traveling about Arkham City need not be done on foot or primarily by grappling hook. The game's developer, Rocksteady, laid out the city to take advantage of Batman's ability to grapple to a ledge and then launch off that point into a long glide. Theoretically, you could go from one end of Arkham to the other in this way, I was told way back at Comic-Con.
While midair, however, Batman might want to interrupt his cruise to dive-bomb the goons below, as we see throughout this five-minute video released today. Use of dive-bombing and glide can also, in a misdemeanor violation of Newton's laws, prolong your flight.
Spoiler alert: You hear The Joker's voice at 0:56.