Chapman's sectional map of Illinois.
MLA
Chapman, Silas. Chapman's Sectional Map of Illinois. Silas Chapman, 0AD. https://collections.library.yale.edu/catalog/15814398.
APA, 6th edition
Chapman, S. (0 C.E.). Chapman's sectional map of Illinois. [Maps]. Silas Chapman, https://collections.library.yale.edu/catalog/15814398.