Just took a look at O'Hare
http://www.satellite-sightseer.com/id/1568
This will be one crazy high detail area and it's best left for last or something, with a proper mesh for the complex taxiway system.
I can go on all day adding airports based on addon requests in the meantime. San Fran area is going to be challenging enough as I will learn how to manipulate alpha layers to get the land to sea transitions to play right with global textures.