There's something I've been wondering for a while, and that is how car navigation systems work. Do they all work the same, or do different companies have different ways of going about it?

The reason I ask is because of these point I was going to post in another thread:

The main thing I notice in my dad's car is that when we leave our house, about 70% of the time the nav will have the car going in a completely wrong direction, different every time. We live about a mile from the Potomac river, and sometimes the nav system will actually show the car driving through the river This astonishes me. It usually takes about a mile of driving before it suddenly snaps back into place and starts working again. Still, in the middle of the trip, it will get confused about which direction he's going in.

My Honda, on the other hand, has an Alpine system that has only gotten off track once in the 3 years I've had it, and that was right after getting out of the 3rd level of an under-building parking garage. However, I have not once seen the system lose direction. Only placement.

Why is this?