Why do some photos taken with iPhone camera not have stored GPS coordinates?

Question

I have an app that allows a user to upload photos from his camera roll only if the photo has stored GPS coordinates. I was wondering what causes some of these photos- taken on iPhone camera- to not have a stored location. Thanks in advance.

Answer 1

I can think of at least four different ways to get photos without GPS coordinates associated:

1. Screenshots - seem to not have any geo information associated
2. Downloaded / imported photos - from Mail, or apps like 9gag for example.
3. Photos taken during active airplane mode

Most uncertain about the last one:

4. Photos taken where there simply is no GPS available, e.g. deep inside a mountain?