An airport in the middle of town draws city planners like moths to a flame. No need to worry about finding a ride to the terminal; it's right there. Unfortunately, cites have this nasty little habit of being filled with these things called "buildings" and unless you build before the city shoots up, a large area is bombed out in a war, or due to all the sea freight moving downriver, a new aerodrome in the middle of town is a bit tricky.
That didn't stop visionaries like Mr Charles Clever from coming up with ideas like dropping an aerodrome in the middle of Clapham Junction. Buildings in the way? Then put the runways on top of the buildings like spokes on a wheel.
Popular Science in November 1939 went Mr Clever one bettter and imagined a two hundred storey skyscraper with a giant airport on the roof complete with Zeppelin terminal.
Beautiful. It's a pity the designer forgot about those nasty cross winds.