Danzer, Gerald (1984). "George F. Cram and the American Perception of Space". Chicago History. 13 (1): 32–46. ISSN0272-8540 – via Proquest.
Cook, Karen S. (2015). "Wax Engraving". The history of cartography. J. B. Harley, David Woodward, Matthew H. Edney, Mary Sponberg Pedley, Mark S. Monmonier. Chicago: University of Chicago Press. pp. 1701–1704. ISBN0-226-31633-5. OCLC13456456.
worldcat.org
Cook, Karen S. (2015). "Wax Engraving". The history of cartography. J. B. Harley, David Woodward, Matthew H. Edney, Mary Sponberg Pedley, Mark S. Monmonier. Chicago: University of Chicago Press. pp. 1701–1704. ISBN0-226-31633-5. OCLC13456456.
