Car Navigation without GPS

I have an idea- was wondering if it is possible and what are its pros and cons.

The idea is that of a vehicle navigation system without GPS. The system will use the digitized map of the area (city, state) for guidance, which it will store in non-volatile memory. Before starting the journey, the route-to-be-taken-map will be selected from the total map and stored in memory. There will be an angle-of-steering-rotation sensor connected to the steering wheel, that will monitor the angle of rotation of the wheel all through the journey. The speed will also be monitored continuously. Both these variables will be monitored with respect to time. By using these variables, i.e. instantaneous speed, instantaneous angle-of-steering-rotation, a route-traveled plot can be prepared, which is to be updated every second. This will show the present position of the vehicle in the area, superimposed on the area map, on a monitor fitted on the dashboard.

If by any chance, the contact of the tyres with the road is lost, the driver has to go to the nearest town/village and then feed the location name into the system. The system will then start re-plotting the route-traveled map by taking that location as a reference. The screen will again start showing the correct position of the vehicle in the area.

This route-travelled can will be compared to the stored digitized map in real time. Thus, if there are any excursions from the desired path in either direction, an aural or pictorial alert can also be given to keep the driver on course.

This can be a boon to those areas, which don't have access to satellite based GPS. It will also be helpful in wartime situations, when the satellites are either blocked or knocked out.