Airports are uniquely represented by their IATA airport code and ICAO airport code. IATA 3-letter airport codes are typically abbreviated of their names, such as MAD for Madrid Barajas International Airport. Exceptions to this rule are, for instance, O’Hare International Airport in Chicago (retains the code ORD from its former name of Orchard Field) and some named after a prominent national celebrity, e.g., John F. Kennedy, Paris Charles de Gaulle, Istanbul Atartuk , etc. The ICAO 4-letter airport identifier codes uniquely identify individual airports worldwide. Usually, the first letter of ICAO codes identify the country. In the continental USA, the first letter is \(K\). In Europe, the first letters is either \(L\) or \(E\).