Getting that to work consistently is a real pain in the ass. I drive around Europe a lot and I'll download maps to save on roaming data and often I've downloaded a place and my phone still wont be able to generate directions for me. I don't know if I miss little spots that are needed to connect my end points or if it is just broken. It's been this way for quite a while. I've downloaded routes themselves and had that fail as well.
It has a transactional guarantee of "maybe". I would _definitely_ not rely on this functionality for anything other than non-critical or time sensitive casual navigation on roadways.
When I'm out in the bush, I need my device to be up and working locally. It seems that stuff designed in SV just assumes the lifestyle of 100% connectivity is universal.
Gaia GPS is fantastic. You can mix and match layers, and specify what bounds you want to download for a trip.
Right now I've got 3 GB stored locally, some of that for the usual locations that I wander out of connectivity, and some for a trip next week.
Garmin (formerly Delorme) Earthmate despite their other issues is great for state or province wide vector maps. Not as great for fine navigation and tracking (as it's designed to be paired with and control an InReach), but good for point of interest exploration.
I love Gaia on my iPhone and iPad, but I’ve had real problems with map layers not displaying lately. MapBox Streets and Gaia Streets are both hosed and I can’t figure out why.
Forgive the potential facetiousness of my reply because I know it's not exactly what you're asking for, but if you know where you'll be then save the images somehow. Knowing how flakey Apple Maps is without connectivity, if it's important, then I'll take screenshots of the route before I leave, for the same reason I'll print out important slides of a presentation because even a lo-fi plan B is better than total failure.
Are online maps really that much better than a paper map? The only real improvement is the same as that of mp3 over carrying a walkman and bunch of tapes. There's not much beyond that, for all the hype.
Like so many things (Amp/SPA websites; social media; 24 hour rolling news…) they seem to me to not really improvements over what we had, because someone somewhere tried to lock the customer in. Maybe that's just misanthropic luddite me.
Typical satnav devices work fine without internet connectivity. Of course, such a device won't work if it can't connect to satellites providing positioning data but I think that was not what you had in mind when you said "connectivity".
Trailforks is power hungry but is great if you're on-trail. If you're off trail, hilariously Garmin Explore I think is pretty good, you can download Topo and USGS maps, but logging in isn't working right now :) so look elsewhere
Here Maps for vehicle nav. If you download the maps of course. OSMAnd and Windy Maps w/ on device maps for outdoor. Here is also used on Audi's satnav I think. The voice is the same and the missing roads are the same.
Osmand has full offline navigational functionality for free and uses as well as contributes to the open street maps data set instead of a proprietary one. I've used it to save my bacon a few times when I tried to start navigation well away from cell coverage.
The Graphhopper routing service is great for cycling. It even has different bike profiles, walking and hiking. The bike profile is essentially a touring bike and the algo is tuned to avoid slopes. Road bike sticks to the road, MTB uses backroads and footpaths. Hiking prefers more scenic route even if they're longer.
There are also quite a few offline navigation and hiking/adventure apps. Standalone GPS devices can be rugged but that's about their only advantage. It's silly to complain about smartphones not working off the grid when all you have to do to fix that is tap a button before you leave home.
And given that GPS services are free, it's fantastic when you need to find your way around a town in a foreign city. I was using it to find my way around the medina in Marrakech last year.
