Geohash

Turning a latitude and longitude into a short base32 string, demoing the p/moul/x/daily/geohash library.

One point, at growing precision

Jutland, Denmark, at 57.64911, 10.40744:

 1  u
 2  u4
 3  u4p
 4  u4pr
 5  u4pru
 6  u4pruy
 7  u4pruyd
 8  u4pruydq
 9  u4pruydqq
10  u4pruydqqv
11  u4pruydqqvj

Every character adds five bits and every prefix is itself a valid geohash of the same place, so truncating one zooms out. Two hashes sharing a long prefix are close together, which is what lets an avl tree keyed this way answer "everything near here" with a range scan and no geometry at all.

Two more places, at the length each one needs:

• Null Island (0, 0): s0000
• Leon, Spain (42.6, -5.6): ezs42
• Jutland, Denmark (57.64911, 10.40744): u4pruy

Next: /cell for the box a hash names, /neighbors for the eight cells around one.