Geohash does not provide a one-to-one mapping. Geohashes "u150gxv4" and "u150gxv5" and others, decode to (50.8,4.38).

Also, geohashes of many proximal points are very different (see http://geohash.org/f840p2n2p3 and http://geohash.org/dxfpzryrzq although these locations are 1 meter apart)

Also, while geohashes are great for computer storage, they are not so much for human memory.