Navigation systems get their location (in longitude/latitude) from GPS. The DVD's or CD's contain the map information. RavenFan_94, I think you and I have the same Navi systems, because it our cars do not have MOST bus technology.
http://e-partssales.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=00004490078&Category_Code=POTEBXCM
I have the cd's that came with it. They are a bit out of date, but still work great.
Have a good trip.
Larez2