To answer the question in the comments, my technique for this was pretty basic (I'm a little apprehensive to reveal it as I'm afraid it will take away the "magic", so to speak, but it is really quite simple). I used some Japanese patterned paper I picked up from the art store for the background, which I scanned (it comes in packages, you get about 12-15 different patterns for $12.00). Then, I drew two different sets of buildings and scanned them in separately. I then masked the two building sets, and copied them onto the file containing the patterned paper. I moved the buildings to where I wanted them, combined them with the background (or flattened the layers), and then changed the colour of the background. Ta-da! Pretty simple, but time consuming.
