Offline maps, stored on your smartphone or tablet, just need a GPS signal, no cell coverage needed. I can fire up my osmand app and see a map of my current location in just a few seconds.

I reviewed the open source osmand app in this thread, repeated below. There's other offline map apps available now, but this is the one I've used. For locating places by name, or browsing for local restaurants or stores, google maps is very good, but it needs a data connection.

From Nov 2015:
I have the inexpensive pay version of osmand (it's osmand+). A one-time fee (maybe $6?) to download any number of state or region maps. And I purchased the countour and elevation overlay (maybe $2?) The free version has a limit of 10 state downloads.

If I'm doing driving directions, I normally use google maps if I have a data connection. They have updated traffic and better routing calculations. But osmand is fast to load and uses the previously downloaded map files.

If your phone has a separate data card, configure Osmand to store it's maps there. If you have a lot of states, it adds up to quite a bit of storage. I have 2.5 GB with maybe 10 states loaded.

Here's an example of osmand screen shots, Mount Mitchell, near Asheville NC:

zooming in. The elevations are in meters, not feet. It shows different types of roads in different colors, and bike trails show in dark blue.





Contour lines every 10 meters (33 feet).



Zoomed way in, with a location marker that can be named and saved. More details appear as you zoom in--the museum building and bathrooms symbol, for instance.