Is there a map that shows how lat/long maps to locality/county/sublocality/subadmin and possibly covered area?
No, each lat/lng is done individually to match an address. (Using Google)
Note: Reverse geocoding is an estimate. The geocoder will attempt to find the closest addressable location within a certain tolerance; if no match is found, the geocoder will return zero results.
I don't use Apple products so cannot comment on Apple Maps (they do need to improve a lot).
Nokia (they own Navteq) and MapQuest are also a good contenders for reverse geocoding
Tiger Census 5-Digit ZIP Code Tabulation Areas (ZCTAs) Cartographic Boundary Files is where you want to go. If you want to pay and have a much higher accuracy rate use Maponics or Navteq data