I don't know how to solve that unless you actually have your idea of having "meet" on HN itself.
It is extremely frustrating when you recognize a like-minded individual, you want to engage with them, befriend them, for the benefit of both, and you're just unable to because they neglected to add some contact detail/link/hint.
The first 2 digits of the zip code are an area, but a large one.
XX is the départment, one of the two major administrative divisions in France. It is made of communes - "cities".
It can be rather small like 75 - Paris, or of the size of half of Massachusetts (about 11000 km2).
The YYY means that you are in this department but there is no distance relationship between the numbers. And then of course you can have a city in 78 a km away from a city in 92 and 30 km away from one in 78.
It is true that this at last gives a rough estimation of where someone is
On a related note, for any HNers (or hackers) in/around Austin, TX that want to meet, I'd be happy to help organize a meetup in Austin, if you're interested in connecting.
Would love an easier and semi official way to get things started.