The International Civil Aviation Organization establishes sets of 4-letter location indicators which are published in ICAO Publication 7910. These are used by air traffic control agencies to identify airports and by weather agencies to produce METAR weather reports. 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. Examples of ICAO location indicators are RPLL for Manila Ninoy Aquino Airport and KCEF for Westover Joint Air Reserve Base.
The International Air Transport Association uses sets of 3-letter IATA identifiers which are used for airline operations, baggage routing, and ticketing. There is no specific organization scheme to IATA identifiers; typically they take on the abbreviation of the airport or city such as MNL for Manila Ninoy Aquino Airport.
In the United States, the IATA identifier usually equals the FAA identifier, but this is not always the case. A prominent example is Sawyer International Airport, Michigan, which uses the FAA identifier SAW and the IATA identifier MQT.
The Federal Aviation Administration location identifier (FAA LID) is a three- to five-character alphanumeric code identifying aviation related facilities inside the United States, though some codes are reserved for, and are managed by other entities.:§1–2-1
For nearly all major airports, the assigned identifiers are alphabetic three-letter codes, such as SFO for San Francisco International Airport. Minor airfields are typically assigned a mix of alphanumeric characters, such as 8N2 for Skydive Chicago Airport and 0B5 for Turners Falls Airport. Private airfields are assigned a four-character identifier, such as 1CA9 for Los Angeles County Fire Department Heliport. The location identifiers are coordinated with the Transport Canada Identifiers described below.