My (Volvo) car satnav can obviously identify where it is and uses a DVD-loaded map to direct me - however it recently went 'off-grid' when I decided to drive directly between two locations rather than use the main roads.
I obviously missed a turning (I was on country roads with few signposts) but, instead of recalculating (as usual when I divert from the specified route) it just went dumb until I retraced my steps and regained the designated route.
I don't know whether this was a GPS communication failure or whether the roads weren't on the mapping system - it could have been that the roads were unadopted as they led to private properties (though not signposted at such - just country farms.
Does my satnav communicate with the US system or the European system?