Fun google maps shot of Detroit:
detroit - Google Maps
All that empty space used to be houses.
Not sure why I spaced on this, but I said GM headquarters was the only auto industry left in the city, but that's not entirely true. GM has an assembly plant in Hamtramck, which isn't the city proper, but might as well be, Chrysler has two small plants, and while it's much smaller than it once was the Rouge is still operating. The auto industry has in large part abandoned the city, but I mis-spoke as to what degree.