Cassini's map of France. An encyclopedia of the territory
When: 14.10.2026 11:00
Where: 48.859963, 2.357272
Organizer: Admin
In 2021 and 2025, the National Institute of Geographic and Forestry Information (IGN) transferred to the National Archives the archive collection related to the Academy's map of France, better known as the Cassini map of France.
This remarkable collection consists of calculations, writings, minutes but also copper plates and original prints recounting the making and life of this map between 1750 and the 1950s. A collection whose exceptional nature allows us today to reveal little‑known aspects of a work of universal scope; a work designed by four generations of astronomers and cartographers: the Cassinis.
The art of science
First map surveyed “geometrically” at the scale of an entire country, the Kingdom of France, at the time the most powerful and populous in Europe, its creation is admirable on more than one level. It is, first, the fruit of a continuous state will that, with Louis XIV and Colbert, Louis XV then Bonaparte, decides and sustains the project; even if, from 1756 to 1793, a private company partly finances it. It involves the use of innovative scientific techniques, for the method and the instruments, which link it to the creation of the Academy of Sciences in 1666 and the Paris Observatory in 1667. It is born from the perseverance of scholars who implement it until 1815, alongside the dynasty of the four Cassinis from 1669 to 1793. It results from field work followed by restoration by engraving, both meticulous, standardized, sometimes difficult, and of very long duration, from the surveys of Abbé Picard in 1668 to the last verified surveys in 1790. It is also extraordinary in its final deployment, in space of course since the 181 assembled sheets measure more than twelve meters high by eleven meters wide; but also in time, because from the first work in 1668 to the ultimate use of the copper plates in the 20th century, almost three centuries pass!
An extraordinary adventure
The construction of the Cassini map of France constitutes a true epic. From the astronomer to the bookseller, passing through the engineer‑cartographer, the verifier or the engraver, each profession must work with great precision and in accordance with the detailed instructions given by Cassini III in 1744 in his *Description géométrique de la France*. Surveys, toponymy, calculations, drawings, signs… all steps are scrupulously observed. Lens‑objectives, eyeglass graphometers, quarter‑circles… cutting‑edge instruments for the time are used.
This scientific field work lasted more than 70 years before reaching its completion in 1815. A titanic undertaking based on an unprecedented method: triangulation, which allows distances to be measured with great precision by linking fixed points such as towers, bell towers, hills.
Inhabitants are invited to collaborate, notably to name the mapped places. They sometimes do so reluctantly, because behind the “participatory” enterprise they sense the royal will to better manage but also to better control the kingdom. For science, however, these new methods of work will enable the creation of the first complete territorial map of France, a true encyclopedia of the territory.Prestige and posterity
This cartographic monument will be disseminated in a remarkable material diversity, from the ordinary copy to the most prestigious. The role of booksellers here is of great importance. Some offer the map with a multitude of possibilities: coloring, mounting, binding, case, hanging rod…
The exceptional quality of certain copies presented in the exhibition, including one on silk, reflects the eminence of their owner, such as King Louis XVI or Queen Marie‑Antoinette. The gigantism of the Cassini map of France is matched only by its lasting use; the most striking being the creation of the Departments in 1790, for which it serves as a cartographic base. Other administrative uses persist to this day, such as those concerning rights related to mills. Its contribution to current environmental history or archaeology is equally essential. A scientific adventure of universal scope, an exceptional cartographic monument, the Cassini map of France becomes a model for Western cartography, renewing its methods.
Tags: cartography, history, exhibition, lecture
Source: https://www.paris.fr/evenements/la-carte-de-france-de-cassini-une-encyclopedie-du-territoire-118002
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