Geohash36

Version 0.3.1-18-g41749f0

Geohash36 is a complete solution for geohashing coordinates. What is a geohash? For example, the coordinate pair 40.689167, -74.044444 (NY City) produces a slightly shorter hash 9LVB4BH89g, which can be used in the URL http://geo36.org/9LVB4BH89g

The main usages of Geohashes are

• as a unique identifier
• represent point data e.g. in databases

In order to describe any location on the planet we normally use Longitude and Latitude geo coordinates. While working with two variables like this is fine, it is prone to certain issues such as how to control arbitrary precision, ease or querying, means of finding locations of proximity, having just one unique identifier and so on.

Out of this reason Gustavo Niemeyer created the Geohash [1][2] algorithm. It is a hierarchical spatial data structure which subdivides space into buckets of grid shape. The two coordinate variables are turned into one local perceptual hash, in which similar spaces share more significant string similarity (from left to right).

This allows very easily to query for similar regions by left to right character matching and the calculation of promimity by for instance edit distance. One can also imagine a efficient data structure which utilizes a TRIE to store such coordinates.

Original Geohash algorithm is based on radix 32 system which leaves us with certain problems. Geohash 36 [2] [3], originally developed for compression of world coordinate data, utilizes radix 36 notation allowing for higher precision and leverages a character set designed for electronic storage and communication rather than human memory and conversation.

It uses an case sensitive alphabet of the characters "23456789bBCdDFgGhHjJKlLMnNPqQrRtTVWX" where characters were 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.

Alphabet conversion table [2]

Decimal 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Geohash-36 2 3 4 5 6 7 8 9 b B C d D F g G h H

Decimal 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Geohash-36 j J K l L M n N P q Q r R t T V W X

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) [4].

The Statue of Liberty, at coordinates 40.689167, -74.044444, is encoded as 9LVB4BH89g-m. The reverse decoding equates to 40.689168,-74.044445.

[1] http://geohash.org/

[2] http://en.wikipedia.org/wiki/Geohash

[2] http://en.wikipedia.org/wiki/Geohash-36

[3] http://geo36.org/

[4] http://www.pubnub.com/blog/wp-content/uploads/2014/05/ProximityChat1.jpg

By running gem comand

gem install geohash36

or by adding to Gemfile

gem 'geohash36', git: 'https://github.com/clothesnetwork/geohash36'

As library

2.1.2 :001 > require 'geohash36'
 => true
2.1.2 :002 > coordinates = { latitude: 40.689167, longitude: -74.044444 }
 => {:latitude=>40.689167, :longitude=>-74.044444}
2.1.2 :004 > hash = Geohash36.to_geohash( coordinates )
 => "9LVB4BH89g"
2.1.2 :005 > resolved = Geohash36.to_coords( hash )
 => {:latitude=>40.689168, :longitude=>-74.044445}

or from the command line

~# geohash36

Commands:
  geohash36 coords GEOHASH [ACCURACY]  # Get coordinates for geohash with specified accuracy
  geohash36 hash LATITUDE LONGITUDE    # Get geohash36 from coordinates
  geohash36 help [COMMAND]             # Describe available commands or one specific command

~# geohash36 hash 40.689167 -74.044445

9LVB4BH89g

~# geohash36 coords 9LVB4BH89g

Latitude: 40.689
Longitude: -74.044

1. Fork it ( https://github.com/clothesnetwork/geohash36/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

• Oleg Orlov
• Bjoern Rennhak

Please refer to the COPYING.md and LICENSE.md file.