Lanman, Jonathan T., On the Origin of Portolan Charts. Chicago: The Newberry Library, 1987. ISBN 0-911028-37-4. 28x2lcm., xii, 56pp., illustrated, paper. (60 W. Walton St., Chicago, IL 60610, $6.00)

The late Dr. Lanman's thesis is that the amazingly accurate portolan charts of the Mediterranean were constructed from printed sailing directions.  Others have speculated that their great accuracy reflected an ancient tradition of practical cartography, as distinguished from the urban crowd of armchair academics who were absorbed in their revisions of Ptolemy.  I am not sure he has proven his case, but at least he employed quantitative techniques.  Charles Hapgood tried this years ago, but Lanman, who curiously does not refer to Hapgood, has employed them more extensively.  I am certain that digitizers and image processing techniques will eventually be commonly used in interpreting map sources.

David C. Jolly, 1989