system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't I get service when high up on a plane, but when I take a picture with my iPhone, it knows exactly where I am and tags my location?
gpt
It's using GPS to determine your location, not cell towers.  As long as you have 3 satellites you can get a signal for you can get a position, the more satellites you are able to 'see' the more accurate the position.

Likewise, if you're in an area where there is no cell coverage, you can still use the GPS in the phone to get your position or use an application that has offline maps.

Edit to add: if you have 'airplane mode' set on the phone it should disable all radios including GPS, and you would not get geo-tagged photos.