I used to drive a volvo at work, the sat nav screen emerged from the dashboard and doubled as a tv for those long hours of standby- all as part of the radio system. Generally the picture would cut out as soon as the wheels were turning, and cut back in at very low speeds (probably to be able to angle the car to get a good picture)
Interestingly there are now screens available, whether on volvo's or not I do not know that show two different images from different viewing angles, the driver can see the sat-nav whilst the passengers can be watching the entertainment system.