Geohash
Geohash is a latitude/longitude geocode system invented by Gustavo Niemeyer when writing the web service at geohash.org, and put into the public domain. It is a hierarchical spatial data structure which subdivides space into buckets of grid shape, which is one of the many applications of what is known as a Z-order curve, and generally space-filling curves.
Geohashes offer properties like arbitrary precision and the possibility of gradually removing characters from the end of the code to reduce its size (and gradually lose precision).
As a consequence of the gradual precision degradation, nearby places will often (but not always) present similar prefixes. The longer a shared prefix is, the closer the two places are.
Service
The purpose of the geohash.org service, launched in February 2008, is to offer short URLs which uniquely identify positions on the Earth, so that referencing them in emails, forums, and websites is more convenient.
To obtain the Geohash, the user provides an address to be geocoded, or latitude and longitude coordinates, in a single input box (most commonly used formats for latitude and longitude pairs are accepted), and performs the request.
Geohash-36
The Geohash-36 geocode is an opensource compression algorithm for world coordinate data. It was developed as a variation of the OpenPostcode format developed as a candidate geolocation postcode for the Republic of Ireland. It is similar in function to the original public domain Geohash code. It is calculated differently and uses a more accurate base 36 (or rather radix 36) representation rather than the original base 32 representation.
Coding Method
Designed for URLs and electronic storage and communication rather than human memory and conversation, it is case-sensitive, using a 36 character alphabet: "23456789bBCdDFgGhHjJKlLMnNPqQrRtTVWX".
Character Conversion:
Characters are chosen to avoid vowels, vowel-like numbers, character confusion, and to use lowercase characters which are generally distinct from their uppercase equivalents in standard typefaces.
The code can be of varying length and thus precision. Each character represents a further subdivision in a 6 by 6 grid - starting at the North-West (top-left) coordinate and continuing, row by row, to the South-East (bottom-right). Neighbouring coordinates have largely similar encodings and generally vary at the rightmost characters only; however extreme edge cases exist where neighbouring coordinates are on opposing sides of a grid division. Codes sort logically but not in ordinary coordinate order.
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