Use Apple Maps offline

From experimentation, if you choose one of three routes to a destination, Apple Maps will guide you along that route without cellular data connection turned on. If you deviate from that route because you prefer another route, it wil persistently show that it is recalculating, but never actually do it. It has the map info to show where you are, but apparently, the intelligence to recalculate the route is not resident on the phone.

Thank you for your links. I actually did quite a bit of internet searching before posting. It's possible that I overlooked a specific detail in one of the pages, but my question was very specific -- exactly what kind of browsing of a route is needed to capture the required detail for turn-by-turn voice navigation. Some of the webpages are a bit dated, and my understanding is the Apple Maps has improved a lot over recent years.

What I observed was that the deactivation of the data connection did not interfere with the navigation so long as you use the route that was chosen prior to deactivating. However, it's not just the route that is stored. The surrounding map info is stored too, because it shows where you are even if you wander from the route. There is no voice navigation instructions to bring you back onto the route, so I'm guessing (and only guessing) that the voice instructions that are generated (and stored) are only for when you're on the route. This is consistent with the fact that a new route to get you back onto the originally planned route is not calculated for you if you wander off the original route. The map info is there, it's just that the algorithms to calculate routing doesn't appear to be on the phone.