Even more: because you didn't click on your contact's name in your contact list?

I click on my dad's name in my contacts list and it shows his home phone, cell phone, and address. Next to each is an icon allowing me to "call the phone number" or "launch Navigation for this address".

That's one option, but I have a Tomtom, and many other cars use built-in GPSs. I was thinking of the more general case, not just for me.