An imaging system suitable for use with a vehicle based global positioning system includes an imaging sensor and a control. The imaging sensor is positioned at the vehicle and may face generally forwardly with respect to the direction of travel of the vehicle. The control may be operable to provide a record of vehicle movement since the last position data derived from the vehicle based global positioning system. The imaging system may also or otherwise be suitable for use with a vehicle based magnetic compass system. The imaging system may be operable in combination with a magnetic field sensor of the magnetic compass system to provide a substantially continuously calibrated heading indication, which is substantially resistant to local magnetic anomalies and changes in vehicle inclination. The imaging sensor may be associated with one or more other accessories of the vehicle.