Process for road trajectory data of memorization for a car navigation system

This method consists of recording in a RAM memory 8, together with the data in digital form for each location of roads on maps, index numbers which are sequentially assigned to specific locations on the route for each route and card numbers each assigned to each card and course numbers assigned to each drive on each card. When the vehicle moves, it also monitors number card and course number while locating the current position of the vehicle (sensors 1, 2, 3) and are stored (processing system 4) a previous card number, a previous route number and an index number previous if the current card number is different from the previous card number or the current course number is different from the previous route number. the invention reduces the number of data road path storing.