MLA

of Strategic Services. Research, United States. Office, and Analysis Branch. Ilocos Sur. Northern Portion. 1945. https://collections.library.yale.edu/catalog/15238634.

APA, 6th edition

of Strategic Services. Research, U. S. O., & Branch, A. (1945). Ilocos Sur. Northern portion. [Maps]. https://collections.library.yale.edu/catalog/15238634.