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Open Location Code is a technology that gives a way of encoding location into a form that iseasier to use than latitude and longitude. The codes generated are called Plus Codes, as theirdistinguishing attribute is that they include a "+" character.

The technology is designed to produce codes that can be used as a replacement for street addresses, especiallyin places where buildings aren't numbered or streets aren't named.

Plus Codes represent an area, not a point. As digits are addedto a code, the area shrinks, so a long code is more precise than a shortcode.

Codes that are similar are located closer together than codes that aredifferent.

A location can be converted into a code, and this (full) code can be converted back to a location completely offline, without any data tables to lookup or online services required.

Codes can be shortened for easier communication, in which case they can be used regionally or in combination with a reference location that all users of this short code need to be aware of. If the reference location is given in form of a location name, use of a geocoding service might be necessary to recover the original location.

Algorithms to

• encode and decode full codes,
• shorten them relative to a reference location, and
• recover a location from a short code and a reference location given as latitude/longitude pair

are publicly available and can be used without restriction. Geocoding services are not a part of the Open Location Code technology.

• Demonstration site
• Mailing list
• Comparison of existing location encoding systems
• Open Location Code definition

Codes are made up of a sequence of digits chosen from a set of 20. Thedigits in the code alternate between latitude and longitude. The firstfour digits describe a one degree latitude by one degree longitudearea, aligned on degrees. Adding two further digits to the code,reduces the area to 1/20th of a degree by 1/20th of a degree within theprevious area. And so on - each pair of digits reduces the area to1/400th of the previous area.

As an example, the Parliament Buildings in Nairobi, Kenya are located at6GCRPR6C+24. 6GCR is the area from 2°S 36°E to 1°S 37°E. PR6C+24 is a 14by 14 meter wide area within 6GCR.

A "+" character is used after eight digits, to break the code up into two partsand to distinguish codes from postal codes.

There will be locations where a 10-digit code is not sufficiently precise, butrefining it by a factor of 20 is i) unnecessarily precise and ii) requires extendingthe code by two digits. Instead, after 10 digits, the area is dividedinto a 4x5 grid and a single digit used to identify the grid square. A singlegrid refinement step reduces the area to approximately 3.5x2.8 meters.

Codes can be shortened relative to a location. This reduces the number of digitsthat must be remembered, by using a location to identify an approximate area,and then generating the nearest matching code. Shortening a code, if possible,will drop four or more digits from the start of the code. The degree to which acode can be shortened depends on the proximity of the reference location.

If the reference location is derived from a town or city name, it is dependenton the accuracy of the geocoding service. Although one service may place"Zurich" close to the Google office, another may move it by a hundred meters ormore, and this could be enough to prevent the original code being recovered.Rather than a large city size feature to generate the reference location, it isbetter to use smaller, neighbourhood features, that will not have as muchvariation in their geocode results.

Guidelines for shortening codes are in thewiki.

Recovering shortened codes works by providing the short code and a referencelocation. This does not need to be the same as the location used to shorten thecode, but it does need to be nearby. Shortened codes always include the "+"character so it is simple to compute the missing component.

• 8F+GG is missing six leading characters
• 6C8F+GG is missing four leading characters

The subdirectories contain sample implementations and tests for differentlanguages. Each implementation provides the following functions:

• Test a code to see if it is a valid sequence
• Test a code to see if it is a valid full code(not all valid sequences are valid full codes)
• Encode a latitude and longitude to a standard accuracy(14 meter by 14 meter) code
• Encode a latitude and longitude to a code of any length
• Decode a code to its coordinates: low, high and center
• Shorten a full code relative to a location
• Extend a short code relative to a location