https://blog.sldx.com/blockchain-proof-of-location-7af5eb8073c1#.5jrrhgyx8
"As with proof of existence in time, an “event” is defined by a hash H. Perhaps it’s a hash of a photo you at the Great Wall of China and you want to prove you were there, rather than downloaded an image from the internet and photoshopped yourself into it."
...
"So similar to proof existence in time, presenting four hashes is a one-sided bound. They define what’s known as a future light cone. The four hashes are not known by anyone before the satellites transmit them, so the event lies within this cone, and cryptographically cannot lie within the past light cone"
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"Now let’s go one ladder rung deeper into the rabbit hole. Let’s imagine that instead of the GPS satellites, the network of satellites are more akin to bitcoin nodes."
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"Finally, one doesn’t actually need to do this with satellites. It could be done with cell phones and cell towers on the surface of the Earth using triangulation."
A very novel idea that leverages existing technology. The original article gets a bit technical but a lot of it is normal english.