So, I got a used Galaxy Nexus a short while ago, which is the first smart phone I've ever had. It's an older phone, but works okay. I installed Android 6.0.1 on it (actually LineageOS 13). I did not install Google Play on it, in the futile hope that I might be able to keep some shred of info from them (I did ultimately install Yalp Store, though).

The challenge I set out for myself recently was to get some sorta offline GPS map thing set up. I discovered a very good app for this called OsmAnd~. Recommended for fans of open-source who may wish to cut down on data usage.

This app uses Open Street Map. I downloaded the map for the province of Ontario in Canada (which I live in). I enabled GPS in the settings (rather than battery saver mode). Anyway, it works great, without any need to be connected to the internet.

I use navmii, an offline mapping app, got me to scotland and back to wiltshire, and all round turkey, reccomended!

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i totally recommend OsmAnd~.
it's feature-packed, i'm sure there's nothing that comes close to that, proprietary or open.
a little tricky to get through the UI at first, but don't give up, you'll soon find the few settings you need to access more often.

searches "just work" - just like with google maps etc.

one can even edit nodes in a rather intuitive way, did it twice already (requires an account of course).

the app has improved A LOT in the last 3 years or so, so if you tried it then (and didn't like it), try it again.
caveat: it's not exactly lightweight.

what goes for osmand~, also goes for openstreetmap itself.
it has well evolved from another nerdy "Open-something" project to a serious alternative to google & co.
here, in the capital area of a scandinavian country, it is being used by the official public transport route planner, and i'm seeing it more and more often on other (commercial) sites.
pretty sure they pay a few people to add data to the pool - it is getting more and more complete (strangely, i can access much more data with OsmAnd~ than with openstreetmap.org web interface).