Airport names are often abbreviated by codes, including IATA codes and ICAO codes, that are only a few characters in length. Knowing them can be useful for orientation, booking or conversation.
The International Air Transport Association defines a three-letter code for airports and a two-letter code for individual major airlines. These codes, which are intended to be globally unique, are used for ticketing, for booking flights and on baggage tags. It's useful to know the code of the airport you are travelling to:
Using the codes can make entering destinations on airline web sites quicker. On check-in, they're useful as a quick visual check that the luggage tag is sending your belongings to where you are travelling, or that the airline has not made a last minute change. Many airports are known by their code and referenced by local public transport with them and thus the codes can be useful when communicating with taxi drivers. To give just one example, the most convenient bus line to Tegel Airport in Berlin is line TXL. They may also appear in diverse contexts as a colloquial nickname for the city which the airport serves.
In general, IATA assigns two-letter codes to airlines and three-letter codes to airports; three-letter codes for non-aviation facilities (such as rail stations with no associated airport) most often begin with Q, X or Z. Codes beginning with Y have for historical reasons mostly been assigned to Canadian airports.
ICAO codes are assigned by the International Civil Aviation Organization, a specialized agency of the United Nations. These four-letter codes are used by aviators for flight plans and navigation; they are separate and different from IATA codes, which are generally used by travel companies for airline timetables, reservations, and baggage tags. For example, the IATA code for London's Heathrow Airport is LHR and its ICAO code is EGLL. ICAO codes are commonly seen by passengers and the general public on flight-tracking services, though passengers will more often see the IATA codes, on their tickets and their luggage tags.
In general IATA codes are usually derived from the name of the airport or the city served, while ICAO codes are distributed by region and country. Far more aerodromes (in the broad sense) have ICAO codes than IATA codes, and to add to the confusion IATA codes (because of their use for ticketing) are sometimes assigned to railway stations. ZYP, for example, is Penn Station in New York City.
The first letter of the ICAO code identifies a geographic region, while the second letter usually identifies an individual country or region of a country within that region. Canada and the US Lower 48 mostly assign ICAO codes which match the same airport's IATA code, by adding a leading 'C' (Canada) or 'K' (USA 48). In other countries, there may be anywhere between a moderate correlation to no correlation between the IATA and ICAO codes.
While IATA codes for any given airport rarely change and sometimes even preserve an anachronistic former name (IATA: PEK for the main airport of Beijing for example), ICAO codes may and frequently do change when an airport comes under the control of a different country or government. For example, Berlin Schönefeld Airport remained IATA: SXF but changed its ICAO code upon German reunification as it passed from the GDR to the Federal Republic of Germany.
As IATA is used by travel companies for ticketing and baggage handling, an airport with no scheduled flights may have an ICAO code but no IATA code. There's no corresponding IATA tag for KXTA, the ICAO airport code for Area 51 – a closely-guarded military test strip at Groom Lake, Nevada which is not open to civilians.
There are other identifiers in use; national rail carriers (such as Amtrak) have been known to assign their own non-standard codes to train stations on their own lines and agencies of national governments will assign a location identifier to even the tiniest private landing strip - even if there are no other facilities, no passenger terminal, no tickets and no IATA tags.
In some cases, there's nothing there but a bit of open lake suitable for a float plane; a water aerodrome is open water used regularly to land seaplanes or amphibious aircraft, but typically has no facilities and only a regional location identifier (LID). For instance, "Yellowknife Water Aerodrome" holds a national location identifier (TC LID: CEN9) as Air Tindi Ltd's favourite seasonal spot to land on Great Slave Lake; when a carrier stops using the spot, the identifier is normally revoked.
Other identifiers include: