Most apps these days (even Google maps) allow you to download maps to your phone for offline use. The GPS in your cellphone will work without a cell signal.Not sure where on the earth you are, but keep in mind terrain and it's affect on signal. Any time I use a phone app that is cell tower and or cell phone dependent, I tend to loose signal / real time tracking randomly while in heavily wooded areas. My handheld GPS is always on point.
Sent from my XT1585 using Tapatalk