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Open Location Code

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The Open Location Code (OLC) is a geocode system for identifying an area anywhere on the Earth.[1] It was developed at Google's Zürich engineering office,[2] and released late October 2014.[3] Location codes created by the OLC system are referred to as "plus codes".

Open Location Code is a way of encoding location into a form that is easier to use than showing coordinates in the usual form of latitude and longitude. Plus codes are designed to be used like street addresses, and may be especially useful in places where there is no formal system to identify buildings, such as street names, house numbers, and post codes.[4]

Plus codes are derived from latitude and longitude coordinates, so they already exist everywhere.[5] They are similar in length to a telephone number – 849VCWC8+R9, for example – but can often be shortened to only four or six digits when combined with a locality (CWC8+R9, Mountain View). Locations close to each other have similar codes. They can be encoded or decoded offline. The character set avoids similar looking characters, to reduce confusion and errors, and avoids vowels to make it unlikely that a code spells existing words. Plus codes are not case-sensitive, and can therefore be easily exchanged over the phone.[6]

Since August 2015, Google Maps supports plus codes in their search engine.[7] The algorithm is licensed under the Apache License 2.0.[8] and available on GitHub.[9]

Google states that plus codes are accepted as postal addresses in Cape Verde,[10] parts of Kolkata,[11] and the Navajo Nation.[12]

Specification

The Open Location Code system[13] is based on latitudes and longitudes in WGS84 coordinates. Each code describes an area bounded by two parallels and two meridians out of a fixed grid, identified by the South-West corner and its size. The largest grid has blocks of 20 by 20 degrees (9 rows and 18 columns), and is divided in 20 by 20 subblocks up to four times. From that level onwards division is in 5 by 4 subblocks. The table shows the various block sizes at their maximum near the equator. The block width decreases with distance from the equator.

Block sizes of Open Location Codes
Code length 2 4 6 8 + 10 11
Block size 20° 1° 0.05° (3′) 0.0025° (9″) 0.000125° (0.45″)
Approximately 2200 km 110 km 5.5 km 275 m 14 m 3.5 m

The full grid uses offsets from the South Pole (–90°) and the antimeridian (–180°) expressed in base 20 representation. To avoid misreading or spelling objectionable words, the encoding excludes vowels and symbols that may be easily confused with each other. The following table shows the mapping.

Mapping of Open Location Codes
Base 20 digit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Code digit 2 3 4 5 6 7 8 9 C F G H J M P Q R V W X

The code begins with up to five pairs of digits, each consisting of one digit representing latitude and one representing longitude. The biggest blocks have just two digits. After 8 digits, a plus sign "+" is inserted in the code as a delimeter to aid with visual parsing. After 10 digits at each subdivision, subblocks are coded in a single code digit as follows:

Division of subblocks in Open Location Codes
longitude →
latitude →
 R V W X
J M P Q
C F G H
6 7 8 9
2 3 4 5

Areas larger than an 8-digit block can be specified by replacing an even number of trailing digits before the + sign with the digit 0, with nothing after the + sign.

Example

Consider, for example, zooming in on the Merlion (N 1.286785, E 103.854503) in Singapore. It lies in the block around the equator bounded by -10° South and +10° North, and between 100° and 120° East. It has offsets 80° from the South Pole, and 280° from the anti-meridian; or, 4 and 14 as first base-20 digit, coded as "6" and "P". Thus, the code is "6P". This may be padded as 6P000000+

Now, refine this block to a subblock between 1° and 2° N and 103° and 104° E. This adds 11° and 3° to the SW corner. So the base-20 coordinate codes added are "H" and "5". The result is padded to 6PH50000+.

After four further refinements, one lands on Merlion park as 6PH57VP3+PR.

The next step requires us to divide the square so far used, to refine the position into a 4-by-5 grid, and finding the cell to which the coordinates are pointing. This is the cell named "6". Therefore, the resulting Open Location Code is: 6PH57VP3+PR6.

Usage with Plus codes

When using the code in conjunction with Google Maps or Google's site Plus.codes, it is common to omit the first 4 characters from the code and add an approximate location, such as a city, state, or country. The above example, then, becomes 7VP3+PR6 Singapore.

Other geocode systems

References

  1. ^ "Plus codes". Plus.codes. Retrieved 3 November 2018.
  2. ^ "Open Location Code". Openlocationcode.com. Archived from the original on 1 March 2018.
  3. ^ See Open Location Code Github and Open Location Code forum.
  4. ^ The Open Location Code website provides an overview. The document "An Evaluation of Location Encoding Systems" provides a rationale.
  5. ^ Specification: "Open Location Code: An Open Source Standard for Addresses, Independent of Building Numbers And Street Names"
  6. ^ "Open Location Code: Addresses for everything, everywhere". Google-opensource.blogspot.ch. Retrieved 3 November 2018.
  7. ^ "Plus codes: A new way to help pinpoint places on the map". Google-latlong.blogspot.in. Retrieved 3 November 2018.
  8. ^ "google/open-location-code". GitHub.com. Retrieved 3 November 2018.
  9. ^ "google/open-location-code". GitHub.com. Retrieved 3 November 2018.
  10. ^ https://plus.codes/benefits
  11. ^ "Plus Codes | Addressing in Kolkata" – via YouTube.
  12. ^ "The Navajo Nation is getting addresses, thanks to an open-source mapping program used in urban India". The Salt Lake Tribune. 2019-10-25.
  13. ^ "google/open-location-code". GitHub. Retrieved 3 November 2018.
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