The History of Cartography Project’s sixth volume, covering the twentieth century, came out three years ago. Edited by Mark Monmonier, it comprised two physical books and nearly two thousand pages and had a list price of $500. That physical edition is still available (e.g. on Amazon), but as of this month it’s available online for free in PDF form, like the first three volumes in the series. (Volumes four and five are still being prepared; volume four, covering the European Enlightenment, is slated to arrive in 2019.) [NLS]