Include the primary contributer(s) in the author position and use parentheses to identify their contribution – with maps, this is usually ‘cartographer.’
Contributer Lastname, First Initials (If available. Otherwise use Organization) (Cartographer). (Year). Description of Map OR Map Title [Map].
Oregon Department of Geology and Mineral Industries (Cartographer). (1981). Geologic map of the Monmouth and Sidney quadrangles, Oregon [Geologic map]. Retrieved from http://www.oregongeology.org/sub/publications/GMS/gms018_2.pdf
United States Department of the Army Corps of Engineers (Cartographer). (1942). Coos Bay, quadrangle, 15-minute series [map]. 1:62,500. AMS 1170 I- Series, V792. Washington, DC: U.S. Geological Survey.
EROS Data Center (Cartographer). (1983). Annotated landsat 1 MSS image of Palmer Land and George VI Ice Shelf [map]. 1:500,000. In Williams, Jr., R. S., & Ferrigno, J. G. (Eds.), Satellite Image Atlas of Glaciers of the World, Antarctica. Washington, DC: U.S. Geological Survey. (p. B116)