Someone please correct me if I have this wrong, but as I understand it, your GPS app in your phone needs to access data for turn-by-turn directions and route planning.
If you store the maps on your device, it will use the GPS w/o data to tell you where you are, but that's all (and might be enough for you).
App descriptions are not clear on this, it seems to take some digging to distinguish between "here I am" functions, and" turn-by-turn navigation" functions.
The typical handheld GPS device has the routing/planning and turn-by-turn built in. Phone apps go to the cloud for that stuff, so need a data connection. Pre-loading the maps may be able to help cut down on the amount of data, but that might all be app dependent.
-ERD50
Not with Navigon. As an experiment, I turned off cellular data and wifi on my phone, opened Navigon, entered a random destination, and the app could still find my route and give me turn by turn directions. All you need is a GPS signal, just like for a Garmin device.
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