Google Maps does not provide metadata about geographical data used for geocoding or routing. This could lead to some astonishment when the user see the routing results in Google Maps. For example a route from Hungary to Bulgaria will direct through Italy using ferry connections and lasting over 3000 km and 1 day and 15 hours. The reason for this behaviour is not well documented or presented to the user. Google Maps does not have routing relevant data (or the proper quality of data) for several countries. For example it is not possible to route in Serbia or Bulgaria. Therefore routes running through these countries will results in detours.
An other interesting example is Moscow. Yon can calculate routes in Moscow but not in rural Russia. Google provides a document where all countries are listed and you can find out about their current map functionality.
