MLA

Conover, Allan D. Railroad Map of Wisconsin / Prepared for the Railroad Commissioner by Allan D. Conover C.E. Milwaukee Litho. & Engr. Co., 1881. https://collections.library.yale.edu/catalog/15814562.

APA, 6th edition

Conover, A. D. (1881). Railroad map of Wisconsin / prepared for the railroad commissioner by Allan D. Conover C.E. [Maps]. Milwaukee Litho. & Engr. Co., https://collections.library.yale.edu/catalog/15814562.