A vehicle navigation system, comprising: a GPS receiver (104; 302) carried aboard a vehicle and subject to interruptions of signal transmissions from orbiting navigation satellites (308; 702); a database carried by the vehicle; a dead-reckoning computer coupled to the GPS receiver (104; 302) and configured to provide range and heading information computed during periods of said signal interruptions, and such that vehicle navigation solutions are continually available through a screen display (102; 320) to a user; wherein, change in range and change in heading information related to movements of said vehicle are propagated by the dead-reckoning computer from absolute position information periodically obtained from the GPS receiver (104; 302), with the dead reckoning results alone sometimes being output as vehicle navigation solutions; wherein, a combined GPS and dead reckoning position is corrected for drift away from a road segment by feedback correction; characterised in that the navigation system further comprises: wheel-tick sensors (120; 122; 124; 126) coupled to the dead-reckoning computer and configured to provide rotational data related to the turning of individual wheels (112; 114; 116; 118) that carry said vehicle; wherein, estimates of true radii of said individual wheels (112; 114; 116; 118) are combined with said rotational data from the wheel-tick sensors (120; 122; 124; 126) to generate, the change in range and the change in heading information; a network server arranged to communicate wirelessly with the vehicle through a wireless network; and a road map database, comprised by the network server, arranged to provide map information for a limited local area on request by the vehicle to the database carried by the vehicle through the wireless network, wherein the amount of map information provided to the database carried by the vehicle is calculated in order to allow corrections in drifts away from a road segment by feedback corrections to be provided for around five minutes of vehicle travel time at the local speed limits. a GPS receiver (104; 302) carried aboard a vehicle and subject to interruptions of signal transmissions from orbiting navigation satellites (308; 702); a database carried by the vehicle; a dead-reckoning computer coupled to the GPS receiver (104; 302) and configured to provide range and heading information computed during periods of said signal interruptions, and such that vehicle navigation solutions are continually available through a screen display (102; 320) to a user; wherein, change in range and change in heading information related to movements of said vehicle are propagated by the dead-reckoning computer from absolute position information periodically obtained from the GPS receiver (104; 302), with the dead reckoning results alone sometimes being output as vehicle navigation solutions; wherein, a combined GPS and dead reckoning position is corrected for drift away from a road segment by feedback correction; characterised in that the navigation system further comprises: wheel-tick sensors (120; 122; 124; 126) coupled to the dead-reckoning computer and configured to provide rotational data related to the turning of individual wheels (112; 114; 116; 118) that carry said vehicle; wherein, estimates of true radii of said individual wheels (112; 114; 116; 118) are combined with said rotational data from the wheel-tick sensors (120; 122; 124; 126) to generate, the change in range and the change in heading information; a network server arranged to communicate wirelessly with the vehicle through a wireless network; and a road map database, comprised by the network server, arranged to provide map information for a limited local area on request by the vehicle to the database carried by the vehicle through the wireless network, wherein the amount of map information provided to the database carried by the vehicle is calculated in order to allow corrections in drifts away from a road segment by feedback corrections to be provided for around five minutes of vehicle travel time at the local speed limits. wheel-tick sensors (120; 122; 124; 126) coupled to the dead-reckoning computer and configured to provide rotational data related to the turning of individual wheels (112; 114; 116; 118) that carry said vehicle; wherein, estimates of true radii of said individual wheels (112; 114; 116; 118) are combined with said rotational data from the wheel-tick sensors (120; 122; 124; 126) to generate, the change in range and the change in heading information; a network server arranged to communicate wirelessly with the vehicle through a wireless network; and a road map database, comprised by the network server, arranged to provide map information for a limited local area on request by the vehicle to the database carried by the vehicle through the wireless network, wherein the amount of map information provided to the database carried by the vehicle is calculated in order to allow corrections in drifts away from a road segment by feedback corrections to be provided for around five minutes of vehicle travel time at the local speed limits.