Very cool! However, I would like something similar without Google or Apple or Microsoft ever knowing what I downloaded. Is there a privacy-respecting mapping app that supports ahead-of-time downloading of map data that actually works well?
OSMand is what I use 95% of the time for offline navigation. I first discovered this when I realized you couldn't use Google Maps for navigation in Serbia in 2015. The other 5% of the time I use Google Maps or Waze directly or manually enter its route suggestions as navigation waypoints into OSMand.
Here maps is run by a consortium of european car manufacturers. They let you download entire countries even.
IIRC they have their roots in navteq, which was acquired by nokia in their heyday. They have really good level of detail in my corner of the world in the middle-east, FWIW.
