MLA

Association, Gettysburg Battlefield Memorial. Gettysburg and Vicinity : Showing the Lines of Battle July, 1863. Gettysburg Memorial Battlefield Association, 0AD. https://collections.library.yale.edu/catalog/15811156.

APA, 6th edition

Association, G. B. M. (0 C.E.). Gettysburg and vicinity : showing the lines of battle July, 1863. [Maps]. Gettysburg Memorial Battlefield Association, https://collections.library.yale.edu/catalog/15811156.