Zone of Interior

A United States military term used historically to refer to the contiguous United States, as opposed to overseas theaters of operation. In declassified UFO documents, sightings and intelligence reports are often categorized as occurring either within the ZI or overseas. This designation helped the Air Force Office of Special Investigations (AFOSI) and Project Blue Book allocate jurisdictional resources.

A critical jurisdictional and geographic classification in early USAF Project Blue Book and intelligence files.