All parts of Volumes 1, 2, 3, and 6 are accessible online at no cost.
http://www.press.uchicago.edu/books/HOC

The University of Chicago Press publishes The History of Cartography in print, e-book, and online formats. Currently, Volume 1, Volume 2 (Books 1, 2, and 3), Volume 3, and Volume 6 are available to the public online. All content–text, footnotes, images and captions, bibliographical index, and general index–may be accessed at no cost through downloadable and searchable PDF files. The remaining volumes will be similarly available within three years of print publication.

PDFs of chapters or entry groups from History of Cartography  volumes had received over 3.5 million hits online by December 2019.