Geocode: Difference between revisions

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A '''geocode''' is a [[code]] that represents a geographic entity ([[___location]] or [[Geographical feature|object]]). It is a [[unique identifier]] of the entity, to distinguish it from others in a [[finite set]] of geographic entities. In general the ''geocode'' is a [[human-readable]] and short identifier.

Typical geocodes (in bold) and entities represented by it:

* ''Country code'' and subdivision code. Polygon of the administrative boundaries of a country or a subdivision. <br />The main examples are ISO codes: [[ISO 3166-1 alpha-2]] code (e.g. '''<code>AF</code>''' for [[Afghanistan]] or '''<code>BR</code>''' for [[Brazil]]), and its subdivision conventions, such as [[ISO 3166-2:AF|{{mono|1=AF}} subdivision codes]] (e.g. '''<code>AF-GHO</code>''' for [[Ghor province]]) or [[ISO 3166-2:BR|{{mono|1=BR}} subdivision codes]] (e.g. '''<code>BR-AM</code>''' for [[Amazonas (Brazilian state)|Amazonas state]]).

* ''DGG cell ID''. Identifier of a cell of a [[discrete global grid]]: a [[Geohash]] code (e.g. ~0.023&{{nbsp;}}km² cell '''<code>6vjyngd6vd23gq</code>''' at the Brazil's [[NationalGeographical Congress of Brazilcentre|Brazilian's centercentroid]]) or ana [[Open Location Code|OLCPlus Code]] code (e.g. ~0.004&0002{{nbsp;}}km² cell '''<code>58PJ642P58Q8XXXX+4XX</code>''' atwithin the same pointarea).

* ''Postal code''. Polygon of a [[postal code|postal area]]: a [[Código de Endereçamento Postal|CEP]] code (e.g. '''<code>70040</code>''' represents a Brazilian's central area for postal distribution).

The [ISO&nbsp;19112:2019 standard<ref>"ISO 19112:2019 — Geographic information — Spatial referencing by geographic identifiers", "Section 3.1.2 — Geographic identifier", https://www.iso.org/standard/70742.html ISO 19112:2019] standard</ref> (section 3.1.2) adopted the term "geographic identifier" instead ''geocode'', to encompass long labels: ''spatial reference in the form of a label or code that identifies a ___location''. For example, for ISO, the country name “People's Republic of China” is a label. Some authors, such as the United States Census Bureau,<ref>"Understanding Geographic Identifiers (GEOIDs)", https://www.census.gov/programs-surveys/geography/guidance/geo-identifiers.html</ref> use the abbreviation "GEOID" as a synonym for ''geocode''.

Geocodes are mainly used (in general as an [[Primitive data type|atomic data type]]) for [[labelling]], [[data integrity]], [[geotagging]] and [[Spatial database#Spatial index|spatial indexing]].

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== Geocode systemSystem ==

The set of all geocodes used as unique identifiers of the cells of a [[Tessellation#Voronoi tilings|full-coverage]] of the [[Terrain|geographic surface]] (or any well-defined area like a country or the oceans), is a '''geocode system''' (also named ''geocode scheme''). The [[Syntax (programming languages)|syntax]] and [[Semantics (computer science)|semantic]] of the geocodes are also components of the system definition:

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|last1=DeLozier|first1=Jochen L.

|date=2007|title=Toponym resolution in text: annotation, evaluation and applications of spatial grounding

|url=httphttps://www.era.lib.ed.ac.uk/handle/1842/1849|publisher=University of Edinburgh|hdl=1842/1849}}</ref> Any standardized system of toponym resolution, having codes or encoded abbreviations, can be used as ''geocode system''. The "resolver" agent in this context is also a ''geocoder''.

Sometimes names are translated into numeric codes, to be compact or machine-readable. Since numbers, in this case, are name identifiers, we can consider "numeric names" &mdash; so this set of codes will be a kind of "system of standard names".

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When subdivisions's names are expressed as codes, and code syntax can be decomposed into a parent-child relations, through a well-defined syntactic scheme, the geocode set configures a hierarchical system. A geocode fragment (associated to a subdivision name) can be an abbreviation, numeric or alphanumeric code.

A popular example is the [[ISO 3166-2]] geocode system, representing country names and the names of respective [[Administrative division|administrative subdivisions]] separated by hyphen. For example <code>DE</code> is [[Germany]], a simple geocode, and its subdivisions (illustrated) are <code>DE-BW</code> for [[Baden-Württemberg]], <code>DE-BY</code> for [[Bayern]], ..., <code>DE-NW</code> for [[Nordrhein-Westfalen]], etc. The scope is only the first level of the hierarchy. For more levels there are other conventions, like HASC code– Hierarchical Administrative Subdivision Codes.<ref>{{cite book|author=Gwillim Law|year=2016|title=Administrative Subdivisions of Countries: A Comprehensive World Reference, 1900 Through 1998|publisher=McFarland |isbn=978-0-7864-0729-3|url-access=registration|url=https://archive.org/details/administrativesu0000lawg}}</ref><ref>{{statoids|id=ihasc|title=Hierarchical administrative subdivision codes}}</ref> The HASC codes are alphabetic and its fragments have constant length (2 letters). Examples:

:<code>DE.NW</code> - [[North Rhine-Westphalia]]. A two-level hierarchical geocode.

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|-

| [[What3words]]|| 2013 || globe || encode(latLon) || '''patented''' || grid cell

| patent-restrictions system, converts 3x3 meter squares into 3 words.<ref>{{cite web|title=What3words: Find and share very precise locations via Google Maps with just 3 words|date=2 July 2013|url=https://thenextweb.com/apps/2013/07/02/what3words-a-new-way-to-search-for-and-share-locations-via-google-maps-with-just-3-words-universal-address-system/|access-date=8 July 2014}}</ref> It is in use at [[Mongol Post]].<ref>{{Cite web|url=httphttps://geospatial-solutions.com/mongolia-adopts-what3words-as-national-addressing-system/|title = Mongolia adopts what3words as national addressing system – Geospatial Solutions : Geospatial Solutions| date=June 2016 }}</ref>

|-

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| Geopeg is word-based GPS address, using simple words like London.RedFish. It is a combination of a city and two simple words. It is an open standard geocoding of Earth, currently in development. [https://geopeg.com/demo Geopeg]

|

|-

|[[Dymaxion Geographic Encoding]] || 2024 || globe || encode(latLon,precision) || open standard || triangle

| Based on the Dymaxion map projection, uses a 64-bit unsigned integer to represent locations. Provides global coverage with high precision, achieving nearly 100% utilization of the available bit space. Uses an icosahedron-based triangular grid.

|}

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* In the United States, the American National Standards Institute (ANSI) Codes are often used. ANSI INCITS 446-2008 is entitled "Identifying Attributes for Named Physical and Cultural Geographic Features (Except Roads and Highways) of the United States, Its Territories, Outlying Areas, and Freely Associated Areas, and the Waters of the Same to the Limit of the Twelve-Mile Statutory Zone".

* [[National Topographic System]] in Canada

* [[ONS coding system]] (hierarchical code used in the UK for tabulating census)

===Other standards===