This has been researched before... (Score 2)

This idea has been investigated before. Dorothy Denning calls it "the grounding of cyberspace" There is a chapter on this coauthored by her and Peter MacDoran in the book edited by Peter Denning.

Title of the paper is Location-Based Authentication: Grounding Cyberspace for Better Security

This idea is also explained in her book Information Warfare. The idea is using GPS signatures which are not forward-predictable. As other posters pointed out, that only proves the existence/access to GPS receiver located at some point and time not necessarily the presence of the *individual* there.

WakeTurbulence