Books with overlays are one of my favorite things and Cool Hunting linked to this interesting "book" about cities.
One of the things I hope we see as iPad apps develop, is apps that enable the overlays that used to be in all sorts of books when I was younger. The ability to swipe and go though time on a map, cover a skeleton with muscles, shift a sky around with the zodiac, swipe and get the different characteristics of birds to help narrow down identification are things I look forward to.
