I used to take photos on flights using a GPS receiver or logger.

Now I use a dongle which connects to my camera and has an app which will stream GPS coordinates to the dongle and write them to a file every time I snap the shutter.

I've played around with my iPhone before takeoff, usually opening up the route and zooming in on different portions so that the detailed parts are cached. This lets me have a better idea of where I am during the flight. But I think iOS uses their own maps app and Compass app to represent location data.

I didn't try to download offline maps for Google Maps because it seems you can only download a relatively small tile. That might work for pedestrian or car navigation but not flights because you'd need so many tiles.

It also seems like older versions of iOS had more reliable GPS streams in airplane mode than curren versions.