Apple must have deals with some vendors of very detailed 3D imagery for specific areas – in the Virgin Islands e.g. you can zoom in to see that individual vehicles and boats are bump-mapped and draped.
Apple bought C3 Technologies, a Swedish 3D mapping company back in 2011. It was originally spun out of SAAB (the mapping solution was originally used for missile targeting systems, iirc.)
more info: https://www.youtube.com/watch?v=3apAXzf3JTg