A location identifier is a symbolic representation for the name and the location of an airport, navigation aid, or weather station, and is used for staffed air traffic control facilities in air traffic control, telecommunications, computer programming, weather reports, and related services.
The International Civil Aviation Organization establishes sets of four-letter location indicators which are published in ICAO Publication 7910.
The first letter indicates the region; for example, K for the contiguous United States, C for Canada, E for northern Europe, R for the Asian Far East, and Y for Australia.
The International Air Transport Association uses sets of three-letter IATA identifiers which are used for airline operations, baggage routing, and ticketing.
Private airfields are assigned a four-character identifier, such as 1CA9 for Los Angeles County Fire Department Heliport.
The block beginning with Z identifies United States Air Route Traffic Control Centers.
Most one-digit, two-letter identifiers have been assigned to aviation weather reporting and observation stations and special-use locations.
Since January 2019, the National Civil Aviation Agency of Brazil (ANAC) issues a six-digit designator called Aerodrome Identification Code (Portuguese: Código de Identificação de Aeródromo, CIAD) for each aerodrome.
(These characters are chosen with the same methodology as for IATA codes, i.e. taking three letters of the airfield name, for example ZPU for Zacapu Airstrip.)
Within Russia (and before 1991 within the Soviet Union), there are airport identifiers (внутренний код - internal code) having three Cyrillic letters.
Unlike the IATA codes, they changed when renaming some cities of the former USSR in the 1990s, e.g. Saint Petersburg (formerly Leningrad), which was ЛЕД and became СПТ.
[5] A presentation at the WMO site[6] explains: The National Weather Service uses several schemes for identifying stations.
These typically end in X, such as where Birmingham, Alabama (BHM) had its radar site replaced by one south of the city (BMX), or where the Knoxville (TYS) office was moved to nearby Morristown, Tennessee (MRX).
One system still used by both the Air Force and National Climatic Data Center is the Master Station Catalog or MASLIB code.
Transplanted identifiers tend to be poorly documented, and can cause problems in data systems and software which process historical records and in research and legal work.