ViewRanger is a free to download app. We have used this one many times to get us out of a pickle. ViewRanger provides free access to global maps including OpenStreetMap, OpenCycleMap and aerial imagery.
- Maps are stored on your phone and can be used offline to avoid data/roaming charges
- Zooming in and out allows you to see details more clearly than on paper
- You can choose to rotate maps on screen so they are easier to follow