Country codes are short alphabetic or numeric geographicalcodes (geocodes) developed to represent countries and dependent areas, for use in data processing and communications. Several different systems have been developed to do this. The most famous of these is ISO 3166-1.
The Fédération Internationale de Football Association (FIFA) assigns a three-letter code (dubbed FIFA Trigramme) to each of its member and non-member countries: List of FIFA country codes
The North Atlantic Treaty Organisation (NATO) used two-letter codes of its own: list of NATO country codes. In 2003, the eighth edition of the Standardisation Agreement (STANAG) adopted the ISO 3166 three-letter codes with one exception (the code for Macedonia).
The coding system for car license plates under the 1949 and 1968 United Nations Road Traffic Conventions (distinguishing signs of vehicles in international traffic): List of international license plate codes [1] (http://www.unece.org/trans/conventn/Distsigns_Sept2003.pdf)
the first few characters of call signs of radio stations (maritime, aeronautical, amateur radio, broadcasting, etc.) define the country: the ITU prefix,
Before the 2004 EU enlargement the EU used the UN Road Traffic Conventions license plate codes; since then, it uses ISO 3166-1, with 2 exceptions: EL (not GR) is used for Greece, and UK (not GB) is used for the United Kingdom. [2] (http://eur-op.eu.int/code/en/en-cover.htm)
The Nomenclature des unités territoriales statistiques (Nomenclature of territorial units for statistics, NUTS) of the European Union, mostly focusing on subdivisions of the EU member states
Three-character codes are also used for the United States (xxu), Canada (xxc), and the United Kingdom (xxk) when the state, province or territory, or division is not known, but the country is known, or when it is not desired to code at the lower level.
Thus when using countrycodes to retrieve records, if the code for the entity has changed since the implementation of an earlier code list, it is advisable to specify both the new and previously assigned (historical) codes in the retrieval request if records coded prior to the changes are desired.
In this case, the code for the annexed entity is discontinued, and the annexed entity becomes a reference to the name of the entity whose code is used after the change.
Codes are assigned for both the place of origin and current location of peoples who are in an area other than their permanent homeland, including travelers, temporary residents, aliens, and foreign students.
Codes are assigned for the location of individual named entities, including corporate bodies, buildings and structures, roads, waterways, railroads, monuments, camps, parks, gardens, etc. For government agencies, codes are assigned for the jurisdictions the agencies serve.
In this case, the code for the annexed entity is discontinued, and the annexed entity is assigned the code for the annexing entity.