The basis of hydrographic network 1: 50000 is a project carried out by joint order of the Ministry of the Environment (DMA) and the Catalan Water Agency (ACA). The aim of this project is to obtain digital databases and GIS network watershed of Catalonia for scales 1: 50000. The primary source of information for the elaboration of this theme was based hydrographic network base topographic 1: 50000 (BT-50M v3.0) was defined criteria and topographic database drainage basins, for what has become a task of densification and homogenization. It has kept the artificial network but has not been taken into account in generating basins, and in the case of natural drainage network has added sections connection guarantee continuity of it. This coverage corresponds to the selection of the 0 degree axis of the base network of rivers (xarxa50m), adding those areas corresponding to the selection made so that all points of Environmental Control (Inspection and Control), it is referenced on the same network. Only display areas corresponding to the basins of Catalonia.