You have to use cats to switch between Catwoman and Batman in the main story, but I've seen only seen one group of cats, the ones right next to Catwoman's apartment. It's a hassle to fly back there whenever I want to switch. The game says that there are multiple groups of them, but I can't find more. Where are all of the other cats?
Here are the cat locations in Arkham City:
There's one on the shore near the Joker's side of town. They should be visible on your minimap with a cat icon