Fine example of Van Keulen's chart of South China Sea, from the the exceedingly rare 'secret atlas'.

This exceedingly rare chart was first published by Johannes van Keulen [II] (fl 1720-1755) the grandson of the founder of the van Keulen firm also Johannes van Keulen (1654-1711). In 1753, he produced an additional volume VI to augment his grandfather's famous sea atlas, the 'Zee-Fakkel', containing detailed printed charts for the navigation of the waters from the Cape of Good Hope to Nagasaki. Although the atlas was not commercially sold and only for use on board Dutch East India Company (VOC) ships, the printing of these charts was a considerable departure for the VOC, who had hither to relied on manuscript charts, for fear that printed material would be disseminated to easily, and the Companies competitive edge blunted.

Due to the atlas's commercial sensitivity it became known as the 'secret atlas', and by the lack of extant examples of either the atlas or charts, it would appear that the VOC was adept at keeping it so.