so you're asking for a way to search for people based on profile "metadata" the About box, or time system basically when you say gm, more posts in the time slot concerned.
at least don't use countries https://git.fiatjaf.com/countries there's really nothing else, apart from Japanese relays.
I'm not sure how it would be done or if it's possible since nostr doesn't have a traditional database and I'm not an engineer.
I'm guessing it's kinda of like hashtags. Where your notes or profile would be automatically tagged with USA so all users with the USA tag would have their own country feeds and you would be able to search for npubs using that tag.
As a work around would putting # (location) in your bio work ?
Just wondering as im not a dev either, my knowledge of coding is limted to "it's something people do"😁
