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The Open Location Code (OLC) is a geocode based on a system of regular grids 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 (e.g., 849VCWC8+R9) but can often be shortened to only four or six digits when combined with a locality (e.g., CWC8+R9, Mountain View, California). 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 has supported plus codes in its search engine.[7] The shortened plus code is displayed for a location, may be copied, clicked, or transcribed, and can be entered into the address box (followed by the town or city name if not local and using shortened code) to display the location on the map. The algorithm is licensed under the Apache License 2.0[8] and is available on GitHub.[9]
Plus codes are increasingly being used for addressing purposes in places that aren't well-served by the traditional street address system. This includes the many unnamed streets in Cape Verde,[10] multiple slums in India,[11][12][13] and even some Native American reservations in the United States.[14] In Laxmi Nagar, Pune, the nonprofit Shelter Associates used codes to bring delivery services to specific homes and businesses in the slum for the first time in 2020-21.[12] Plus codes are also being used by the International Rescue Committee in Somalia for immunization and family planning programs.[12]
The Open Location Code system[15] 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 southwest 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.
| Code length | 2 | 4 | 6 | 8 | + | 10 | 11 |
|---|---|---|---|---|---|---|---|
| Block size | 20° | 1° | 0.05° (3′) | 0.0025° (9″) | 0.000125° (0.45″) | ||
| Approximately | 2,200 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.
| Base 10 digit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Base 20 digit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | G | H | I | J |
| 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 delimiter to aid with visual parsing. After 10 digits at each subdivision, subblocks are coded in a single code digit as follows:
| 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.
Consider, for example, zooming in on the Merlion fountain (1.286785°N 103.854503°E) in Singapore, which has Open Location code "6PH57VP3+PR6". 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 (=80/20) and 14 (=280/20) as the first base-20 digits, 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 dividing 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".
BASE20 Formula
Alternatively, use formula BASE(Degrees from South or West * power(20, 4) , 20) in any Spreadsheet or Calculator to compute the OLC Code.
- For (1.286785°N 103.854503°E) in Singapore,
- 1.286785N = 91.286785 from South Pole, in Base20 = 4B.5EE(5) in alphanumeric = which is 6H.7PP in PlusCode digits.
- 103.854503E = 283.854503 from Anti-Meridian, in Base20 = E3.H1G(0) in alphanumeric = which is P5.V3R in PlusCode digits.
- Combining latitude and longitude alternatively, 6P H5 7V P3 PR.
- The last leftover in Base20, (5)/20 latitude and (0)/20 longitude gives 6 in the 4-by-5 grid.
Therefore, the resulting Open Location Code is: 6PH57VP3+PR6.
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". This is supported by the Google Maps app and the plus.codes website, and also by non-Google apps. These short forms of plus codes can be used in lieu of a house number in a neighborhood.
Shortened codes cannot be unambiguously encoded or decoded without context. The specification does not rely on any specific database of contextual reference location place names and their exact locations, but there are a variety of geocoding databases which map names to latitude and longitude. Disambiguation requires narrowing the possibilities to within about 40 km of the referenced location. The coordinates of the user's current location can be also used for context, if applicable.[16][17]
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