This primary source comes from the Records of the Office of the Chief of Engineers.
National Archives Identifier:
305624Full Citation: Fort Sumter...Horizontal Projection. Survd. & drawn by A. H. A. Becker, 1865; ca. 11/1865; Records of the Office of the Chief of Engineers, Record Group 77. [Online Version, https://www.docsteach.org/documents/document/fort-sumterhorizontal-projection-survd-drawn-by-a-h-a-becker-1865, April 26, 2024]