Geohash is a latitude/longitude geocode system invented by Gustavo Niemeyer when writing the web service at geohash. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement A Geocode ( G eospatial E ntity O bject Code) is representation format of a geospatial coordinate measurement used to provide a standard representation org, and put into the public domain.

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 present similar prefixes.

Contents 1 Service 2 Example 2.1 Decode from base 32 2.2 Decode binary to decimal 2.3 Worked example 3 License and patents 4 See also 5 External links 6 References

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. PortalCurrent events International holidays February 2 - Candlemas February 5 - Shrove Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving An, or message board, is a Bulletin board system in the form of a discussion site A website (alternatively web site or Web site, a back-construction from the Proper noun World Wide Web) is a collection of Web pages

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. Geocoding is the process of finding associated Geographic coordinates (often expressed as Latitude and Longitude) from other geographic data such Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement

Besides showing the latitude and longitude corresponding to the given Geohash, users who navigate to a Geohash at geohash. org are also presented with an embedded map, and may download a GPX file, or transfer the waypoint directly to certain GPS receivers. GPX, or GPS eXchange Format is an XML schema designed for describing GPS data between software applications Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth Links are also provided to external sites that may provide further details around the specified location.

Example

Using the hash ezs42 as an example, here is how it is decoded into a decimal latitude and longtitude

Decode from base 32

The first step is decoding it from base 32 using the following character map:

Decimal	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
Base 32	0	1	2	3	4	5	6	7	8	9	b	c	d	e	f	g
Decimal	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Base 32	h	j	k	m	n	p	q	r	s	t	u	v	w	x	y	z

This operation results in the bits 01101 11111 11000 00100 00010. Base 32 or duotrigesimal is a Numeral system with 32 as its base A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Assuming that counting starts at 0 in the left side, and that 0 is even, the even bits are taken for the longitude code (0111110000000), while the odd bits are taken for the latitude code (101111001001).

Decode binary to decimal

Each binary code is then used in a series of divisions, considering one bit at a time, again from the left to the right side. For the latitude value, the interval -90 to +90 is divided by 2, producing two intervals: -90 to 0, and 0 to +90. Since the first bit is 1, the higher interval is chosen, and becomes the current interval. The procedure is repeated for all bits in the code. Finally, the latitude value is the center of the resulting interval. Longitudes are processed in an equivalent way, keeping in mind that the initial interval is -180 to +180.

Finishing the procedure should yield approximately latitude 42. 6 and longitude -5. 6.

Worked example

Here's a worked example decoding 101111001001 into 42. 6. To start with, we know the latitude is somewhere in the range -90 to 90. With no bits, we'd have to guess the latitude was 0, giving us an error of +/- 90. With one bit, we can decide whether its in the range -90 to 0, or 0 to 90. The first bit is high, so we know our latitude is somewhere between 0 and 90. Without any more bits, we'd guess the latitude was 45, giving us an error of +/-45

Each subsequent bit halves this error. This table shows the effect of each bit. At each stage, the relevant half of the range is highlighted in green - a low bit selects the lower range, a high bit the upper range.

The last column shows the latitude, simply the mean value of the range. Each subsequent bit makes this value more precise.

bit	min	mid	max	val
1	-90. 000	0. 000	90. 000	45. 000
0	0. 000	45. 000	90. 000	22. 500
1	0. 000	22. 500	45. 000	33. 750
1	22. 500	33. 750	45. 000	39. 375
1	33. 750	39. 375	45. 000	42. 188
1	39. 375	42. 188	45. 000	43. 594
0	42. 188	43. 594	45. 000	42. 891
0	42. 188	42. 891	43. 594	42. 539
1	42. 188	42. 539	42. 891	42. 715
0	42. 539	42. 715	42. 891	42. 627
0	42. 539	42. 627	42. 715	42. 583
1	42. 539	42. 583	42. 627	42. 605

(The numbers in the above table have been rounded to 3 decimal places for clarity).

License and patents

The Geohash geocode has been put in the public domain by its inventor in the public announcement date, in February 26th, 2008. The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone ^[1]

While comparable algorithms have been successfully patented^[2] and had copyright claimed upon^[3][4], GeoHash is based on an entirely different algorithm and approach.

See also

• Morton number (number theory)
• Natural Area Code
• Maidenhead Locator System

External links

• geohash.org
• Perl module to interact with geohash.org
• Javascript module for encoding and decoding geohashes without interacting with geohash.org and Demo
• Ruby gem for encoding and decoding geohashes without interacting with geohash.org
• Perl module for encoding and decoding geohashes without interacting with geohash.org
• PHP class for encoding and decoding geohashes without interacting with geohash.org
• Python module for encoding and decoding geohashes without interacting with geohash.org
• Proposal for a similar encoding and associated 'geo' URL scheme

References

In mathematical Number theory and Computer science, a Morton number is a single integer value constructed by interleaving the bits or digits of one or more source The Natural Area Code (or Universal Address is a proprietary Geocode system for identifying an area anywhere on the Earth, or a volume of space anywhere around the The Maidenhead Locator System is a scheme used by Amateur radio operators for identifying positions on the Earth

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