Count de Ferraris’s Maps of the Austrian Netherlands (1770s): Cassini de Thury’s Geodetic Contribution

It is generally assumed from something said by the French surveyor Cassini de Thury in his book Relation d’un voyage en Allemagne (1775) that count de Ferraris had incorporated Cassini’s geodetic data into his own maps of the Austrian Netherlands: the manuscript Carte de cabinet (1777) and the Carte marchande (1777). Cassini had carried out a triangulation of the northern part of the Austrian Netherlands during the War of the Austrian Succession (1740–1748), but the extent to which his geodetic data was used by de Ferraris has been the subject of debate. In this article, Cassini’s contribution to de Ferraris’s mapping is reassessed by combining a reinterpretation of the archival record with a metric analysis of de Ferraris’s maps, which shows that de Ferraris used Cassini’s measurements only selectively. This leads to the conclusion that the reason was the limited availability of Cassini’s data and the primarily economic motives for de Ferraris’s use of them.