Hydrographic region

Part of a river basin, and the first order of the hydrographic division of the French territory. This division indeed includes all four parts of the French territory hierarchized according to increasing drainage systems: Hydrographic Region (1st order), hydrographic Sector (2nd order), hydrographic Sub-sector (3rd order), hydrographic area (4th order). A sector is cut into a maximum of 10 sub-sectors and a sub-sector is cut into a maximum of 10 hydrographic areas.