INSTITUT GEOGRAPHIQUE NATIONAL. - Aiguille verte - Chamonix N°6 Sud

Magnificent 1:10,000 scale color printed map of l'Aiguille verte (Chamonix N°6 Sud) based on stereotopographic ground and aerial surveys carried out in the field in 1950 and rendered using the "Poivilliers machine".

The rendering was based entirely on the Vallot and Helbronner triangulations, attached to the new triangulation and to the general leveling, and supplemented by pathways.

By the end of the 1930s, aerial surveys had definitively replaced land-based photographic surveys in the Alps, which were rapidly covered by aerial photographs. At the same time, the SGA included in its program the survey of the Saint-Gervais, Chamonix, and Mont-Blanc sheets of the Carte de France, which represented the entire French part of the Mont Blanc massif.
In June 1939, late enough to take advantage of the limited snow cover and good light conditions, the SGA's specialized squadron carried out aerial coverage of the region: in a Potez 540, the crew flew over the massif up to an altitude of 7,500 meters. It took photos on an average scale of 1:22,000 with a 150 mm focal length lens. The SGA planned to draw up a 1:10,000 map from these surveys, so between 1941 and 1944, the images were reproduced at this scale on a Poivilliers type B stereo topography, with contour lines drawn at ten-meter intervals, even in rocky areas. No preparatory work was carried out to provide a supplementary framework: the rendering was based entirely on the Vallot and Helbronner triangulations, linked to the new triangulation and the general leveling, and supplemented by photogrammetric trails.

The aerial coverage of Mont Blanc was a prestigious undertaking which served to establish the competence of the SGA. (Service Général des Armées), and Colonel Hurault confirmed this strictly prestigious nature when, in 1942, he decided to use this coverage for a special 1:10,000 map of the whole massif, presented in a particularly luxurious style (ten or eleven colours, double shading, etc.).

The delay caused by the war, which meant that it was not possible to complete the map in the field until the summer of 1949, and the gaps observed in the rendering, mainly due to the level of snow cover, which had made it difficult to draw some of the curves and identify the nature of the ground (glacier or rock), meant that two new aerial missions were needed to ensure the precision required to produce such a map. In 1948, oblique photographs of the summits were taken to help with the representation of the rock, and in September 1949, a new vertical coverage was carried out with minimal snow cover at a scale of 1:20,0001469. Despite being discontinued in 1959, with only nine sheets published out of the twenty-four initially planned, the 1:10,000 map of the Mont Blanc massif established itself as the Institute's masterpiece, fulfilling the prestigious mission for which it had been designed while at the same time representing the swan song of a particular approach to high mountain cartography.