True GPS vs Cellular GPS
I thought some might find this useful.
There are two primary consumer sources of GPS navigation, true GPS and cell phone navigation. I'll list the differences and advantages/disadvantages of each.
True GPS - This system/unit receives its signals from the GPS satellite constellation. The signals do not carry maps or anything other than a locator and timing signal. The timing signal is used for synchronization between the satellites and the ground station controlling them. Your receiver determines where you are by comparing signals from at least 3 satellites. The maps on the receiver and its voice are software/firmware loaded onto the device.
Advantages: Navigation everywhere on earth provided you have the maps for the country you're currently in loaded on your receiver device.
Disadvantages: Map updates need to be purchased for your receiver device occasionally (about every 3 years or so if you do a lot of traveling), this is not cheap ($199.00 on current Ram Nav system). As I said above tall buildings in cities can cause problems. Also, signals do not penetrate well into buildings, underwater, or underground.
Cellular GPS: This is a service you pay for on a monthly basis. You are receiving your GPS signal from your service provider. They receive the GPS signal from the GPS constellation for free. They use the signal for timing synchronization of their cellular receivers and transmitters aka towers.
Advantages: Maps are always up to date with the latest information because your phone receives updates as needed. Works great in urban environments and indoors.
Disadvantages: If you are outside your service provider's network you lose GPS capability. You pay a monthly fee for something that is free. You must have a GPS service compatible phone (not all are). Underground and underwater are still not an option.
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