This is interesting. For one, if it uses no cell nor data, then it would need to have the Maps already pre-loaded onto the device. My understanding is that is a ton
of data, probably way more than the D1 can handle.
However, if the app could use the SDCard for map storage, then you'd be in luck.
The other factor would be to see if the GPS radios can be used when the cell / data radios are not connected to a network.
My thoughts are that this can
be done - it's just a matter of finding the right program.
I do know this - newer versions of Google Maps and Nav have an off-line mode, so that you plug in your route, it grabs the info and downloads everything. That way, you could do it all when in the presence of a WiFi signal and then drive.
However, there is still that GPS radio issue, and it would also be an issue for you if you were at one client's office and you decided to go directly from there to another client, requiring a new map. Yes, Waypoints would work, but only
if you knew your total route in the very beginning - any changes to the route would put you at a disadvantage without having WiFi access again.
I found a thread here with similar intentions and some suggestions:
Best offline navigation for US & Canada?
Here are some wites I found via Google:
Android AdvicesBest Offline Navigation Maps Apps for Android Devices -
Next On Google Maps: Offline Navigation, Street Views From The Grand Canyon | Fast Company
CoPilot GPS To Offer Free Offline Navigation Starting In March [Android and iOS]