GPS, or global positioning system, helps guide you to your destination by pinpointing your location and referencing street data. Many smart phones today offer built-in GPS functionality, and you can easily purchase a dedicated GPS unit for your car. But to truly tie the advantages of GPS into your audio system, there's in-dash GPS.
In-dash GPS systems are essentially head units with GPS functionality. They offer large screens for viewing map data and they usually include the same features you'll typically find in a nice receiver, like Bluetooth and USB support.
Naturally, a GPS head unit tied directly into your car audio system will be able to pipe directions straight through your speakers. Today's more expensive cars will offer an in-dash GPS system as an optional extra, but you can always buy an aftermarket unit, too. Just like the head units we covered on the last page, in-dash GPS systems are readily available from a variety of manufacturers. Just keep in mind that they won't be cheap -- expect to pay several hundred dollars for a high-end GPS receiver.