When I’m ON a train, my all time favorite map app is maps.me. It does not use wifi at all! No matter where you are! It uses GPS to locate and display a little blue dot on whatever map I’m looking at on my iPad (in my case; could be a laptop), wherever I am.
And if you download the underlying map files for wherever you are, you can blow up whatever spot on earth you want to look at and get incredible detail. I’ve watched the “me” dot move along the specific TRACK we’re on while moving through freight yards on some of my Amtrak trips.
But note what I said in the second paragraph. It’s free but you must download the files for whichever part of the world you want to see in detail. The app itself only gives you a sort of in between birds eye and view from 30,000’ view of any location. AND it’s important for you to do this BEFORE you leave free wifi. The files you’ll need are large and if you’re already on a train in the middle of nowhere with sporadic wifi at best, it’ll be too late to download the file for somewhere in western Nebraska if that’s what you want to see in detail.
But if you work with it, it’s great! And like I said it’s totally independent of any wifi signal whatsoever.