> Maps and satnav require a web connection.
No they don't require a network at all. The only drawback if there is no network is that the initial finding of the position takes longer. And maps can be downloaded so that they are available offline.
GPS receiver have been working without a "web connection" for ages (e.g. Garmins outdoor devices).
I use my smartphone in "airplane" mode but GPS enabled when hiking. No problems whatsoever.
At least on Android there's a fair number of apps like "osmand" which can download an entire state, province or country vector/map data, in their own semi-proprietary data format derived from public openstreetmap, for truly offline use anywhere you have a GPS signal. It'll even work on a phone that has no SIM card in it.
OsmAnd is also available on iOS: https://apps.apple.com/ch/app/osmand-maps-travel-navigate/id... CoMap also offers offline access to OpenStreetMap data: https://apps.apple.com/ch/app/comaps/id6747180809
Native Apple Maps allow downloading map regions for offline use.