The ICAO (, "IK-KAY-OH") airport code or location indicator is a four-character alphanumeric code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators are used by air traffic control and airline operations such as flight planning. They differ from IATA codes, which are generally used 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 such as FlightAware. In general IATA codes are usually derived from the name of the airport or the city it serves, while ICAO codes are distributed by region and country.