National Surveys and the Rise of Topographic Mapping

Across four generations, from Jean-Dominique Cassini in the late 17th century to Jean-Dominique Cassini IV, whose work concluded in 1793, the Cassini family directed the first triangulation-based survey of an entire nation, resulting in the Carte de Cassini, a set of 182 sheets at a scale of 1:86,400 covering the whole Kingdom of France. Unlike earlier maps compiled from travelers' itineraries and rough estimates, the Cassini survey rested on a systematic chain of triangles, each built from a small number of precisely measured baselines and a large number of angles observed with quadrants and, later, more accurate theodolites, all periodically checked against astronomically fixed reference points to control accumulated error across the whole network.