Charles O. Paullin and John K. Wright's Atlas of the Historical Geography of the United States. First published in 1932. This digital edition developed at the University of Richmond's Digtial Sholarship Lab reproduces all of the atlas's nearly 700 maps. Thanks to the Belfast Telegraph for making the video embeddable. Why the University of Richmond did not is unclear.
In part two of a series on QGIS Boundless' Gretchen Peterson is impressed by the software's capabilities in cartography and "found it was easy and straightforward to create maps."