There is no substitute for a good topo map and old fashioned compass. Knowing how to use them is a basic skill for any outdoors person. With that said, nothing beats being able to bust out your smart phone and immediately know your place on a topo map, and your orientation!
Topo maps does just that. Just pre-download the maps you'll be needing at home, and topo maps will have them ready when you don't have cell coverage. Even without signal, it can put your position on the map using the gps, or you can manually search the map and mark waypoints.
One of my favorite features of TopoMaps is it's ability to stitch together multiple maps. This is super cool if you're hiking near the border between two of the USGS' topomaps.
Other cool features of Topo maps include it's ability to shade what should be visible or invisible, based on a given location. I've found it super handy a lot of times when I'm off trail, backcountry skiing, or just plain turned around and confused about where i am.