MLA

Gast, August, and Co. Map of Nebraska Showing the Union Pacific Railroad Land Grant / Aug. Gast & Co., St. Louis. Aug. Gast & Co., 1883. https://collections.library.yale.edu/catalog/15814808.

APA, 6th edition

Gast, A., & C. (1883). Map of Nebraska showing the Union Pacific Railroad land grant / Aug. Gast & Co., St. Louis. [Maps]. Aug. Gast & Co., https://collections.library.yale.edu/catalog/15814808.