Brussels / 2 & 3 February 2019

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3Geonames.org

An open source Geocoding system for the simple communication of locations with a resolution of 1 m


Encoding geographic coordinates into a string is a trivial thing. Yet, there are many grid based systems (geohash, PlusCodes, Mapcodes), and some even turn the thing into a business (Zippr, What3Words). I agree with the commonly stated motivation that Latitude and Longitude are not sufficient for identifying a place in both an unambiguous and human friendly way. A single string for this pair of numbers is a better representation, if only it can preserve all the information contained in the original latitude,longitude pair, something no existing geo-encoding system does. That's my goal.

Geocode is a one-dimensional location code. It uses a simple space-filling technique to map a two dimensional point (latitude,longitude) to either an alphanumeric string or a geoname triple with no loss of information. It is a one-to-one mapping (no two geocodes map to the same point and no two points map to the same geocode).

Geocode has several advantages over similar systems.

The alphanumeric geocode is short (10 bytes), has higher accuracy (up to 1 meters) and avoids the borderline discontinuities and many to one mappings of other one-dimensional location codes such as geohashes.

Triple geoname codes on the other hand are more memorizable, are intuitively reprentative of the location and are composed of relatively short existing geo names (up to 8 letters).

The first name in a triple geoname code represents the most prominent location name inside a 21,403 kmĀ² area containing the point.

For example, 34.05223,-118.24368 (a location in Los Angeles), is encoded to EKEAJ18E08 or as three geonames: LA-GASPAR-YANSI or as a hybrid code LA-MJKQH4. Another location about 1 m away, say (34.05223,-118.24369), is EKEAJ18E1D or LA-GASPAR-HINGWEN or LA-MJKQI9.

The human readable algorithm uses 146300 geonames from http://geonames.org and http://geonames.nga.mil/gns/html/gis_countryfiles.html with several requirements for the names (chosen to be recognizable, short, easy to pronounce, distinct from each other and evenly spread throughout the earth.) We also shorten geonames to their acronyms whenever possible (LA -> Los Angeles, NY -> New York, etc)

Unlike many grid-based location codes, geocodes represent points not areas. Each geocode maps to a latitude,longitude pair with accuracy up to the 5th decimal point (i.e. 1 meter)

In a nutshell, latitude,longitude values are represented as two linear curves, converted to binary numbers then combined by interleaving their bits. As a result of this technique, similar geocodes are located geographically close together in both alphanumeric and triple geoname formats.

A geolocation expressed as (latitude,longitude) can be converted offline into a geocode, and vice versa using a data structure embeded in the software.

The software is in the public domain to be used without any restrictions.

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Photo of Ervin Ruci Ervin Ruci

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