Traffic information readings corresponding to a vehicle are received, the readings including at least a location. The traffic information readings are compared to information already within a map database, and are used to derive additional map information augmenting or correcting that already within the database, the additional map information subsequently being stored in the database. Additional information that is derived includes the presence of stop signs and traffic lights at intersections, the legality of turns at certain times of day, and the connectedness or non-connectedness of road segments.