Be careful how you use GPS

MrWizard wrote:
GPS device picks up three different satellites, and triangulate your position coordinates, then gets the map info that matches that data
Please explain how magnetic shift changes the orbital position of those satellites
Also for cellular devices, how would magnetic shift change the position of the cell towers

It has to do with direction. When you are in a parking lot and set a point in Google Maps, you have to start moving to have the map arrow point in the right direction. If you have two GPS receivers that talk to each other, one can derive the direction to which you are pointing (heading) while maintaining a fixed position. When on water patrols on the boat using GPS and marine charting software, the arrow just spins around when you stop in one spot in a one Receiver system. On a ship, dynamic positioning relies on multiple GPS receivers.

Try this with your iPhone. Turn off in Privacy the setting for System Services / Compass Calibration. Go into Google Maps and let the Cell Tower triangulation put you on the map. Now turn around in one spot. In my I7, Google Maps does not show which direction I am facing. Go back to Privacy /Location Services / System Services and enable Compass Calibration. Now Google Maps shows me the direction to which i am pointing the iPhone and turns when I do. The compass has assisted the cell triangulation to determine direction. I don't have access to other cell brands.

When one is moving on land or water, the GPS receiver is updating on some built in frequency, like 2 seconds or less frequent. My BadElf receiver is settable for how often I want it to update the triangulation calculation. This governs how frequent the map position is updated and how much detail goes into curves.

Cell service is not available everywhere which is why I use a separate GPS receiver with maps and charts that are resident on the iPhone or iPad. I don't have builtin GPS in the vehicles. The chart plotter in the boat just slowly and randomly spins when completely stopped as it loses the ability the calculate a pointing direction for a fixed position with only one receiver and is not integrated into a compass.

So, a GPS system can operate without a compass. A compass can give you a heading but not position without lots of calculations of multiple directions. A phone with GPS receiver and/or cell triangulation plus compass can give you all sorts of info. A GPS derived position and compass heading can get you out of the woods with no cell service.
Anything that takes down cell service leaves you dependent on a GPS receiver and map plotting. Is a compass and a magnetic point on the earth a system of last resort to find your way out of the wrong turn if the satellites are quiet ?
And of course all of the above could be hooey.