You're right, if IP address 18.104.22.168 is anycast, and you try to connect to that IP, you're going to be routed to the one that is logically closest to you, but you're wrong in that it works as a reliable locator. That same IP address exists in multiple places around the world, so, given just that IP address you have no way of telling where in the world it's coming from. You can perform deep network routing analysis to get what you think is a rough geographical area, but that's all blown away if any part of that link goes through a VPN. Oh, and, IPv6 anycasting works exactly the same way, and it's being used right now. 2001:503:ba3e::2:30 would be a good example of this. Face it, there's simply no way an IP address, or even network mapping, can come even close to using GPS to precisely determine your physical location.