​Accessibility to the air transport system is a complex concept, one that combines notions such as distance, facilities, quality, availability and cost. In this application, ICAO limited itself to the evaluation of distance as a concept, considering that a person has access to international air transport if he or she lives within a 100km radius away from an aerodrome offering direct or indirect scheduled international flights.
 

ICAO used 2015 UN-Adjusted gridded population counts as published by the Socioeconomic Data and Applications Center (SEDAC), which is one of the Distributed Active Archive Centers (DAACs) in NASA's Earth Observing System Data and Information System (EOSDIS). The population data was then aggregated through spatial queries, counting the number of people living within a 100km distance away from aerodromes listed as international by ICAO, or having scheduled flights (ICAO/OAG source) to one of those international airports.​​​​