Geohash Converter

In short A geohash turns a coordinate into a short string by repeatedly halving the world: each bit chooses which half of the current range the point is in, alternating between longitude and latitude, and every five bits become one character of a 32-character alphabet. The consequence people miss is that a geohash is a BOX, not a point. Decoding one returns the centre of that box, and the point that was encoded was merely somewhere inside it. Length is precision: one character is a cell roughly 5,000 km across, five characters is about 4.9 km, eight characters is about 38 m and twelve is under a centimetre. The alphabet is 0–9 and b–z with a, i, l and o removed, because those are the characters people misread — the same reasoning that keeps I and O out of MGRS. The property the whole scheme exists for is that a shorter geohash is always a prefix of a longer one, so points that share a prefix are inside the same larger cell and proximity search becomes a string comparison. The trap that comes with it is severe and worth stating plainly: two points can be a metre apart and share no prefix at all, because a cell boundary runs between them. Any real proximity search has to check the eight neighbouring cells as well, and near the equator and the prime meridian this bites hard.