This is defined as Oakland Airport (OAK) and Istanbul Airport (IST). Codes like Istanbul Airport are often used to just call airports uniquely. Antalya Airport (AYT), Istanbul Sabiha Gokcen Airport (SAW), Dalaman Airport (DLM), Izmir Adnan Menderes Arpt Airport (ADB), Ankara Esenboga Airport (ESB) are other airports near this flight route and their unique identifiers/IATA codes.