WikiCamps lets you download maps to your phone so you do not need to be online to use them. The GPS on your phone will still function with your cell service turned off, or when you simply do not have signal. I used it for my last tour, and for someone who prefers paper maps, I liked using it. I got it to find campgrounds along the tour, and ended up using it as a map. I used it pretty much the way I would use a paper map, with the added benefit that it showed my position on the map.

https://usa.wikicamps.co