The goal of this project is to produce the geological map of northern Algeria at a scale of 1:800,000 indicating information useful to the different domains of hydrogeology, hydrology, climatology, and pedology. The first step was to evaluate the repartition of the different geological formations in each watershed, and the second step was to classify the areas in terms of their permeability. The tools offered by ARC/INFO and ArcView GIS were used to treat and display the result, the groundwater resources of northern Algeria.