I thought this was going to suggest cloud route processing, like Apple Maps/Google Maps/Nokia Here where the GPS is done on the phone, but the routing is done in the cloud.
This is why your iPhone or Android is a hundred or even several thousand times faster to "recalculate" a new route when you take a wrong turn than your trusty, old Garmin. That's also why if you get lost in the middle of nowhere w/out cellular reception, you'll be hoping your old TomTom is still in the glove box - the maps and routing algorithms are all stored on the device itself (though this means the data on it gets outdated and you will need to update it, often for a price).
Yes, you can download a fairly large region and keep it on your device. It also downloads a route when you begin navigating so you could just turn off your wireless once you start and it'll still get you where you are headed.
This is why your iPhone or Android is a hundred or even several thousand times faster to "recalculate" a new route when you take a wrong turn than your trusty, old Garmin. That's also why if you get lost in the middle of nowhere w/out cellular reception, you'll be hoping your old TomTom is still in the glove box - the maps and routing algorithms are all stored on the device itself (though this means the data on it gets outdated and you will need to update it, often for a price).