Now a days there are several apps, Google Maps (and the default Samsung/Google Galaxy 3 Navigation app) that will load a whole section of a state into memory automatically -- which will remain in memory if you get out of wifi range just fine. Just don't turn your device off and please do stay on the app while you are traveling.
Google Maps will remember an entire trip from A to B and keep it in memory as for just as long as you are using the app. Actually, Google Maps is so good it has actually discouraged folks from trying to do some competing apps.
Wifi connection is needed to download a new section of maps. My phone will use the data plan to download in a pinch, but you actually stop in McDonalds, etc periodically which all have wifi now. Obviously tablets need a wifi connection to get a new map.
GPS is really needed for a motorcycle as we get up in mountains, etc. where the triangulate between cell towers trick will not work at all. People in a car can get away with Apple devices that use cell towers only as long as they are on major roads with lots of towers.
Google Maps has done a large upgrade just recently, so it may pay you to do the upgrade to get to the improved trip mapping and off-line map functions of the new Google Maps 8.0.
http://www.androidpolice.com/2014/05/06/google-maps-gets-a-huge-update-to-v8-... Google Maps 8.0 has a new feature where you can have multiple named off-line maps saved, so you can work up your trip by chunks and save each route in a separate named offline map.