The map presented in the atlas is derived from the so-called "Larsonneur map" (Larsonneur et al., 1979). This later was created using data available in 1977 (around 12,000 samples, plus additional information derived from British publications, navigation charts, rock coring and seismic profiles necessary to determine the occurence and the spatial extent of rock outcrops). Each sampled station was assigned a sediment type based on its granulometry and its calcium carbonate content, resulting in 48 possible seabed types, though 3 were not found in the English Channel. Seabed sediment types could also be classified into four main categories (pebble, gravel, sand and mud) based on their granulometry. These criteria enhanced the importance of smaller particles on one hand, and of coarse particles on the other, which both determine the physical and chemical properties of the deposits and hence the biotopic characteristics. Used as layer for habitat.