In my part of the world, Gaia GPS has become the app of choice for navigation using smartphones. It has been used with great success for both adventures, and SAR.

One of the great things about Gaia is that you can import various georefereced datasets into it. Luc Mehl has a nice tutorial on importing satellite data into Gaia. Luc has used Gaia GPS to navigate on an epic 125 mile arctic ice skate trip.

Luc is a very wonderful, friendly guy. He is doing some incredible trips in Alaska. He recently gave a presentation to a group I'm affiliated with. For other amazing adventures, see his website Things To Luc At.

EDIT: Besides trip reports, Things To Luc At also has lots of great info on route planning, self rescue and communication, navigation, etc. It is well worth a Luc!