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From the point of view of a US pilot, it is generally termed as the βassociated cityβ. But this term is only a general term used in publications like the FAA UNITED STATES GOVERNMENT FLIGHT INFORMATION PUBLICATION CHART SUPPLEMENT legend. Every airport recognized by the FAA has an associated city. Title 14, Code of Federal Regulations (CFR), Part 139 (14 CFR Part 139) also uses the term associated city. Even tiny and/or private airports have an associated city. In casual conversation, the term service, services, or servicing city would be just fine. Other governments may have different terminology in their documentation of airports.