ICAO four-letter airport codes are hierarchical. The first one or two letters indicate the country, e.g.: EDDF - Frankfurt (E: Northern Europe, D: Germany) EK

ICAO four-letter airport codes are hierarchical. The first one or two letters indicate the country, e.g.: EDDF - Frankfurt (E: Northern Europe, D: Germany) EKCH - Copenhagen (E: Northern Europe, K: Denmark) VTBS - Bangkok (V: South/Southeast Asia, T: Thailand) KJFK - New York JFK (K: USA) Using ICAO codes, you can make sense of a written out route at a glance. Taking one of the examples from the link: AUY TAH VLI BNE BKK CPH SFJ JAV JUV NAQ becomes NVVA NVVW NVVV YBBN VTBS EKCH BGSF BGJN BGUK BGQQ I.e.: Vanuatu (a few jumps) -> Australia -> Thailand -> Denmark -> Greenland (a few jumps).