This primary source comes from the Records of the Central Intelligence Agency.
Full Citation: Union of Soviet Socialist Republics (USSR) Areas Closed to Foreigners; 11/1949; Published Maps, 1947 - 2015; Records of the Central Intelligence Agency, Record Group 263; National Archives at College Park, College Park, MD. [Online Version, https://www.docsteach.org/documents/document/union-of-soviet-socialist-republics-ussr-areas-closed-to-foreigners, April 17, 2025]