go to google maps and configure Offline Maps. this will let you define and download maps data for areas on your phone, so when you lose data signal, maps can still display (assuming you are using GPS on your phone, if you are relying only on cell signal for location then obviously it will fail).
open google maps
pull up the menu (your places, timeline, etc.)
select offline areas
select custom area
select area, you can shrink, grow and move the box
* if you don't set the map to auto-update, it will be deleted after a time. auto-update will refresh over wi-fi periodically.
* you can create multiple custom areas, so you can make one for Bois d'Arc, and another for Ladonia unit or whatever. Smaller than picking ONE area that covers all the space in between.
*google maps will cut over to downloaded maps automatically if needed.
I have several areas saved on my phone and I think it uses 300 or 400 mb total.