La carte de France de Cassini. Une encyclopédie du territoire

Le Musée des Archives nationales – L’Hôtel de Soubise

A cartographic masterpiece of the 18th century, the Cassini map of France is the first map of France surveyed geometrically at the scale of an entire country. An emblematic historical document, composed of 181 sheets, it is also a monumental work of art measuring eleven metres in width by twelve metres in height. Drawing in particular on a major transfer of records from the IGN to the Archives nationales, the exhibition retraces the history of the map in a new light. In 2021 and 2025, the Institut national de l'information géographique et forestière (IGN) transferred to the Archives nationales the archival collection relating to the carte de France de l'Académie, better known as the carte de France de Cassini. This remarkable collection consists of calculations, writings, drafts, but also the copper plates and original prints recounting the making and life of this map between 1750 and the 1950s. A collection whose exceptional nature today allows us to reveal little-known aspects of a work of universal scope; a work conceived by four generations of astronomers and cartographers: the Cassini family. The art of science The first map surveyed "geometrically" at the scale of an entire country, the kingdom of France, at the time the most powerful and most populous in Europe, its creation is admirable in more ways than one. It is, first of all, the result of a sustained state will which, under Louis XIV and Colbert, Louis XV and then Bonaparte, decided upon and perpetuated the project; even though, from 1756 to 1793, a private company partly financed it. It required the use of innovative scientific techniques, both in method and in instruments, which link it to the creation of the Académie des sciences in 1666 and the Observatoire de Paris in 1667. It was born from the perseverance of scholars who carried it forward until 1815, alongside the dynasty of the four Cassini from 1669 to 1793. It resulted from fieldwork followed by rendering through engraving, at once meticulous, standardized, sometimes difficult, and very long in the making, from the surveys of abbé Picard in 1668 to the last surveys verified in 1790. It is, finally, extraordinary in its final scale, in space of course, since the 181 assembled sheets measure more than twelve metres in height by eleven in width; but also in time, since almost three centuries passed between the first works in 1668 and the last use of the copper plates in the 20th century! An extraordinary adventure The construction of the carte de France de Cassini constitutes a true epic. From the astronomer to the bookseller, by way of the engineer-cartographer, the verifier, or even the engraver, each trade had to work with great precision and in compliance with the guidelines detailed by Cassini III in 1744 in his Description géométrique de la France. Surveys, toponymy, calculations, drawings, symbols… every stage was scrupulously respected. Lens objectives, sighted graphometers, quarter-circles… state-of-the-art instruments for the time were used. This scientific fieldwork would last more than 70 years before reaching completion in 1815. A titanic undertaking based on an unprecedented method: triangulation, which made it possible to measure distances with great precision by connecting fixed points such as towers, bell towers, and hills. Inhabitants were invited to collaborate, particularly to name the mapped locations. They sometimes did so only reluctantly, for behind this "participatory" undertaking, they sensed the royal will to better manage but also to better control the kingdom. For science, however, these new working methods would make it possible to create the first complete territorial map of France, a veritable encyclopedia of the territory. Prestige and legacy This cartographic monument would be disseminated in a remarkable material diversity, from the ordinary copy to the most prestigious. The role of booksellers was, here, of great importance. Some offered the map with a multitude of options: colouring, canvas-backing, binding, case, hanging rod… The exceptional quality of certain copies presented in the exhibition, including one on silk, reflects the eminence of their owners, such as King Louis XVI or Queen Marie-Antoinette. The gigantism of the carte de France de Cassini is matched only by the longevity of its use; the most striking example being the creation of the Départements in 1790, for which it served as the cartographic basis. Other administrative uses persist to this day, such as those concerning rights related to mills. Its contribution to today's environmental history or to archaeology is equally essential. A scientific adventure of universal scope, an exceptional cartographic monument, the carte de France de Cassini became a model for Western cartography, whose methods it renewed.

Source: Paris Open Data ↗