Histoire de la topographie en cartographie : des cartes de Cassini aux cartes IGN

History of topography in cartography: from Cassini maps to IGN maps

Cartography has undergone numerous developments over the centuries, particularly with regard to the representation of relief on maps. In this article, we will explore the different techniques used and the developments in topography in cartography, focusing in particular on Cassini maps, General Staff maps and maps from the National Geographic Institute (IGN). Prepare for an exciting journey through time, discovering the advances that have shaped our understanding of relief in maps of France .

Cassini's maps

In the 18th century, the ambitious project of the Cassini family marked a turning point in the history of French cartography. Between 1756 and 1815, the Cassini family produced a series of detailed maps of France, known as the "Cassini Map". These maps were based on very simple topographical surveys in the field. The agents responsible for carrying out these surveys indicated this by simple enhancements of the watercolor or fine lines representing the inclination of the landscape. It is therefore impossible using Cassini maps to estimate the altitude of a place.
Detail of a Cassini map
Detail of a Cassini map

General Staff maps

In the 19th century, General Staff maps brought new advances in the representation of relief and a great contribution to the history of topography. Commissioned by the French army, these detailed maps were intended for military use. At the beginning of the 19th century, the question of topography and its representation provoked long debates within the topographical commission of the War Depot! Implementation of level curves or adoption of hatching? It will emerge that the surveys will be done using level curves for the sake of precision and that their representation, for the sake of readability, will be done using hatching. The transition from one to the other is very simple: the outline of a hatch follows the shortest path that separates the contour lines!
Detail of a General Staff map
Detail of a General Staff map

IGN maps

In the 20th century, the National Geographic Institute (IGN) played a central role in cartography in France. The IGN continued to develop topographic survey techniques to represent the relief precisely. Cartographers used methods such as photogrammetry, which involves interpreting aerial photographs to create detailed maps. This representation of the topography, thanks to modern printing and coloring techniques, is done using level curves and shadows, making it possible to reduce the load on the map and give a precise overview of the altitude at each point on the map. With the advent of computer technologies, the IGN has also integrated digital cartography into its practices. IGN maps are widely used today, offering precise and up-to-date representations of relief.
Detail of an IGN map
Detail of an IGN map

Conclusion

The evolution of topography in cartography, from Cassini maps to IGN maps, demonstrates the technological advances and innovations that have shaped our understanding of relief in maps. From Cassini triangulation techniques to the topographical surveys of the General Staff maps, including photogrammetry and digital cartography of the IGN, each period brought its own significant advances. Today, thanks to the use of cutting-edge technologies, IGN maps offer detailed and precise representations of the relief, providing essential information for navigation, land use planning and many other areas. Topography continues to evolve, and with it, our ability to represent and understand our geographic environment.
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