The geological map of France to the scale of 1/1 000 000.© BRGM

The Geological Map of France

The Geological Map of France to 1/50000 employed some 3000 geologists for nearly 70 years. In continuity with this major project, BRGM is now developing the French Geological Reference Platform.

After more than two centuries of geological surveys and studies, the BRGM and the entire geoscience community have gained in-depth knowledge of soils and subsoils in France.

The 1/50 000 geological map of France is the most recent outcome of this exemplary work. The mapping programme took 70 years to complete. It employed some 3000 geologists, produced a total of 1 060 maps covering the whole of France at an estimated cost of 300 million euros, and helped to train numerous students in geological fieldwork.

From ground surveys to publication

When the department in charge of the Geological Map of France merged with the BRGM in 1968, the “modern” version of the 1/50 000 geological map, plotted to contour lines on a topographic background, was still in its infancy. 144 maps had been published, or barely 14% of the total.

Since taking over the geological mapping programme, BRGM has handled the entire production chain, from ground surveys to publication. For many years, the geological mapping programme piloted by the BRGM was France’s largest geosciences research programme in terms of human and financial means.

From the geological map of France to the French Geological Reference Platform

The geological map, with all data harmonised and integrating the latest scientific advances in geology, is the foundation for the deployment of the French Geological Reference Platform, the new twenty-year programme that will mobilise the BRGM and all of its academic partners in geoscience research.   

The goal is to provide a digital resource for homogeneous and coherent geological information in 3D on the entire French territory.

Making a geological map

A geological map is the end product of a process of data acquisition and synthesis organised in several stages:

  • compilation and analysis of all existing geological, morphological, geophysical, geochemical and other data;
  • ground surveys performed by geologists, who identify recognisable geological formations on the surface (outcrops) or below ground (by core sampling) to determine their nature (minerals), structure (folds, faults, etc.) and age (fossils). The boundaries of different types of terrain are then plotted onto a topographical map;
  • laboratory analyses of rock samples to determine the age and the chemical and mineral composition of the terrain;
  • contributions from specialised geologists on topics such as hydrogeology (studies of subterranean water tables), materials, minerals, etc. ;
  • creation of a geological map model synthesising all the information collected on the nature, geometry and age of the terrain surveyed.
  • creation of an accompanying legend that defines the map’s regional scope and provides a detailed description of the different geological formations.
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