Map of the County of Northumberland ... by C. & J. Greenwood. Engraved by J. & C. Walker.
MLA
Map of the County of Northumberland ... by C. & J. Greenwood. Engraved by J. & C. Walker. Greenwood & Co., 1831. https://collections.library.yale.edu/catalog/15350000.
APA, 6th edition
Map of the County of Northumberland ... by C. & J. Greenwood. Engraved by J. & C. Walker. (1831). [Maps]. Greenwood & Co., https://collections.library.yale.edu/catalog/15350000.