What the person you're responding to did was a very simple form of locality-sensitive hashing. And even for non-regular grids, as long as they're somewhat regu

What the person you're responding to did was a very simple form of locality-sensitive hashing. And even for non-regular grids, as long as they're somewhat regular (like timezones), you can narrow it down to just a handful candidates that a linear scan will then solve instantly.