Vehicle moves off the route by itself

You're experiencing reflections in the radio signals your 260 is receiving, and it's getting a tad confused. If you use it a lot in urban settings, you might consider an external antenna - which will help it receive stronger signals from the GPS satellites, and better ignore reflected signals.

If you were in downtown NYC, then the tall buildings will interfere with the GPS signals from the satellite. Signals bouncing off the buildings will cause erroneous readings which is what you observed.

I had the same issue with a Nuvi 750 on a rural road in TN. Anyone have any thoughts...............

Nuvi 200 once. I was sitting in the parking lot of my apartment complex and it showed me not only moving, but over Lake Lewisville, which is a bout 3 miles from where I live.

Thank for the response. I was hoping that this was some kind of software upgrade issue. However, this makes sense. Is this normal for most GPS units to encounter this issue? I am not surprised though with regard to the NYC issue. Down there there are so many radio signals floating in such large quantitites that I am surprised that there are not more issues with using radio Freq. based electronics in the city.

Is there no other way to counter act this problem without using an external antenna? Thanks again for everyone's response to this issue.

I live about 1/4 mile from Lake Lewisville and this happened to me on my 760 just a few days ago while I was at home. I know I'm crazy "sometimes" but I'm glad it's not just me it's happening to.

It would have been different if I had chosen the boat as my vehicle.

Go to a open field and park (this will allow the best signal), press the signal strength bars for at least 5 seconds, the satellite screen will appear. At the lower right you will see the accuracy of the combine sats. Notice how this changes as the satellite signal changes. Remember that the GPS satellites are in a geosynchronous orbit around the earth and are consistently changing. About the very best accuracy you can archive with any civilian GPS unit will be about +/- 14 feet.

Remember that the GPS system was developed for military use and that the government has restrictions on civilian accuracy. For aircraft landing GPS ground stations have been establish (WASS) to help maintain an accurate signal but during the final approach aircraft still use local approach instrumentation for instrument landings.

For more GPS information see: http://www.gps.gov/index.html or do a web search for GPS Navigation for many other sights for further info.

The GPS constellation is not geosynchronous. The altitude on these birds is about 180 miles. Geosynch satellites are 22,500 miles up. That's why they are always moving.

Same thing here in downtown Chicago's Loop area. Very tall buildings with little or no signal getting down between them. Even worse, the signal can bounce around a little and make your car pointer jump around. While sitting at a stop light, mine creeped ahead by a full block once. I kept pressing harder and harder on the brake as I sat there. Didn't help.

No, if they were in geosync orbit they would not be changing. The WASS signals do indeed come from Sats in Geosync orbit, the GPS satellites are in much closer orbit and, non equatorial, as you say, constantly changing, which you can observe over time in the sat display (or there are good satellite tracking programs for your PC that will let you see the position and tracks of most satellites.)