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{{distinguish|Address geocoding}}
A '''geocode''' is
Typical geocodes and entities represented by it:
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== Classification ==
[[File:Geocode-exemple1-MASP.png|thumb|420px|
Geocode cells of [[Geohash]], with 8 (blue) and 9 (yellow) digits, a
]]
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* ''Formation'': the geocode can be originated from a name (ex. abbreviation of official name the country) or from mathematical function ([[data compression|encoding]] algorithm to compress [[latitude-longitude]]). See ''geocode system'' types below (of [[#Systems of standard names|names]] and of [[#Systems of regular grids|grids]]).
* ''Hierarchy'': geocode's syntax hierarchy corresponding to the spatial hierarchy of its represented entities. A geocode system can hierarchical ([[#Hierarchical_naming|name]] or [[#Hierarchical_grids|grid]]) or non-hierarchical.
* ''Covering'':
* ''Type of the represented entity'': [[Well-known text representation of geometry|type of geometry]]. Point (the geocode can be translated to a [[Geo URI]]), grid cell (the geocode system is related with a [[discrete global grid|DGG]]) or polygon (typically administrative boundaries delimitations).
<!-- ** grids can be also classified as [[Discrete global grid#Hierarchical grids|''hierarchical'']] or [[Discrete global grid#Non-hierarchical grids|''non-hierarchical'']]-->
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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:
* geocode '''syntax''': the characters that can be used, blocks of characters and its size and order. Example: country codes use two letters of the alphabet (chacacter set A-Z). The most common way to describe formally is by [[regular expression]] (e.g. <code>/[A-Z]{2,2}/</code>).
* geocode '''semantic''': the meaning of the geocode, usually expressed by associating the code with a geographical entity type.
Many syntax and semantic characteristics are also summarized by classification.
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Any geocode can be translated from a formal (and expanded) expression of the geographical entity, or vice versa, the geocode translated to entity. The first is named '''encode''' process, the second '''decode'''. The actors and process involved, as defined by [[Open Geospatial Consortium|OGC]],<ref name="OGC">Definitions of the [[Open Geospatial Consortium|OGC]]'s "[https://www.opengeospatial.org/ogc/glossary/g Glossary of Terms]".</ref> are:
;geocoder: A [[software agent]] that transforms the description of a geographic entity (e.g. ___location name or latitude/longitude coordinates), into a normalized data and
;geocoder service: A geocoder implemented as [[web service]] (or similar service interface), that accepts a set of
;geocoding: Geocoding refers to the assignment of geocodes or coordinates to geographically reference data provided in a textual format. Examples are the two letter country codes and coordinates computed from addresses.<br /> Note: when a [[Address#Current addressing schemes|physical addressing schemes]] (street name and house number) is expressed in a standardized and simplified way, it can be conceived as geocode. So, the term [[geocoding]] (used for addresses) sometimes is generalized for geocodes.
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[[File:States of Germany coded.svg|thumb|200px|right|Germany (<code>DE</code>) with each [[States of Germany|first-level administrative subdivision]] labelled with the second part of its ISO 3166-2 code.]]
[[File:Huc region-edit.png|thumb|right|200px|The 21 top-level 2-digit "region" of hydrologic unit boundaries, using the
Strictly speaking, the "name" related to
type=PhD
|last1=DeLozier|first1=Jochen L.
|date=2007|title=Toponym resolution in text: annotation, evaluation and applications of spatial grounding
|url=http://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,
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" — so this set of codes will be a kind of "system of standard names".
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All cells of the grid have an identifier (DGG's cell ID), and the center of the cell can be used as reference for cell ID conversion into geographical point. When a compact human-readable expression of the cell ID is standardized, it becomes a geocode.
Geocodes of different ''geocode systems'' can represent the same position in the globe, with same shape and precision,
==== Hierarchical grids ====
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Two geocodes of a ''hierarchical geocode grid system'' can use the prefix rule: geocodes with '''same prefix''' represents different parts of the '''same broader ___location'''. Using again the side illustration: <code>TQ 28</code> and <code>TQ 61</code> represents geographically [[Interior (topology)|interior parts]] of <code>TQ</code>, the common prefix.
Hierarchical geocode can be split into keys. The [[Geohash]] <code>6vd23gq</code> is the key <code>q</code> of the cell <code>6vd23g</code>, that is a cell of <code>6vd23</code> (key <code>g</code>), and so on,
In general, as technical and non-compact optional representation, geocode systems (based on hierarchical grids) also offer the possibility of expressing their cell identifier with a fine-grained schema, by longer path of keys.
The uniformity of shape and area of cells in a grid can be important for other uses, like [[Spatial analysis|spatial statistics]]. There are standard ways to build a grid covering the entire globe with cells of equal area, regular shape and other properties: Discrete Global Grid System (DGGS) is a series of discrete global grids satisfying all standardized requirements defined in 2017 by the [[Open Geospatial Consortium|OGC]].<ref>"Topic 21: Discrete Global Grid Systems Abstract Specification", [[Open Geospatial Consortium]] (2017). https://docs.opengeospatial.org/as/15-104r5/15-104r5.html</ref>
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: [[Mapcode]] entrance to the elevator of the [[Eiffel Tower]] in Paris is <code>FR-4J.Q2</code>, where <code>FR</code> is the name-code<ref>
See formal use of ISO country codes in Mapcode
</ref> and <code>4J.Q2</code> is the grid-code. Semantically France is the context, to obtain its local grid.<!-- can be expanded to “France 4J.Q2”-->
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Any ''geocode system'' [[#Systems of regular grids|based on regular grid]], in general is also a shorter way to express a latitudinal/longitudinal coordinate. But a geocode with more than 6 characters is difficult for remember. On the other hand, a [[#Systems of standard names|geocode based on standard name]] (or abbreviation or the complete name) is easier to remember.
This suggests that a "mixed code" can solve the problem, reducing the number of characters when a name can be used as the "context" for the grid-based geocode. For example, in a book where the author says "all geocodes here are contextualized by the chapter's city". In the chapter about Paris, where all places have a Geohash with prefix <code>u09</code>, that code can be removed —. For instance Geohash <code>u09tut</code> can be reduced to <code>tut</code>, or, by an explicit code for context "FR-Paris <code>tut</code>". This is only possible when the context resolution (e.g. translation from "FR-Paris" to the prefix <code>u09</code>) is well-known.
In fact a methodology exists for [[#Hierarchical grids|hierarchical grid-based geocodes]] with non-variable size, where the code prefix describes a broader area, which can be associated with a name. So, it is possible to shorten by replacing the prefix to the associated context. The most usual context is an official name. Examples:
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|-
|[[Open Location Code|Local OLC]] (Cape Verde)|| 2016 || globe || encode(latLon,precision) || free || grid cell
| OLC is used to provide postal services.<ref>(2016-09-08) "Correios de Cabo Verde testam novo sistema de endereçamento da Google",
|-
|[[Postal addresses in the Republic of Ireland#Eircode|Eircode]] (Ireland)|| 2014<ref>{{cite news|author=Dept of Communications |url=http://www.dcenr.gov.ie/news-and-media/en-ie/Pages/PressRelease/Minister-Rabbitte-launches-Eircode-the-new-___location-codes-for-Irish-addresses.aspx |title=Minister Rabbitte launches Eircode the new ___location codes for Irish addresses |publisher=[[DCENR]] |date=28 April 2014 |access-date=2015-07-15}}</ref> || Ireland || encode(latLon,precision) || copyrighted<ref>{{Cite web|url=https://www.eircode.ie/legal|title = Eircode Terms of Use}}</ref> || grid cell
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=== In use, postal codes ===
Geocodes in use, as [[postal codes]]. A geocode recognized by [[Universal Postal Union]] and adopted as "official postal code" by a [[country]], is also a valid postal code.
{|class="wikitable"|
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== Other examples ==
Other geocodes:
* ''S2'':
* ''H3'':
* ''Munich Orientation Convention'': converts lat/lon to metrical monopolar codes for targets, crossings, stations, stop points, bridges, tunnels, towns, islands, volcanoes, highway exits etc.<ref>[https://gssc.esa.int/navipedia/index.php/Step_By_Step_Navigation|Navipedia / ESA]{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
* ''SALB'' (Second Administrative Level Boundaries), by UN
* [[Postal addresses in the Republic of Ireland#OpenPostcode|OpenPostcode]], opensource global algorithm (local adaptations as Irish & Hong Kong postcodes).<ref>{{cite web|title=OpenPostcode.org|url=http://www.openpostcode.org|access-date=10 June 2012}}</ref>
* [[WOEID]]
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===Other standards===
Some standards and name servers include:
A number of commercial solutions have also been proposed:
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{{Geocoding-systems}}
[[Category:Geocodes| for all types of data and information that is used to make a decision about a specific set of information and the information it provides for it
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