San Francisco also puts out an official map, but like many other official maps, it lacks many of the neighborhoods people expect to find: Sunnyside, Japantown, the Tenderloin, Dogpatch, Hunters Point, Mission Bay, Hayes Valley, Miraloma, Cow Hollow... and so in order to give users what they want and expect, Google has to gather data from other sources.

http://sfplanninggis.org/NeighborhoodOrganizations/