The invention is a method for exploitation of a sedimentary basin containing hydrocarbons, including optimized scaling of the geological model. Based on categorical property measurements, a first meshed representation of a formation is constructed reflecting the categorical property measurements. At least one second meshed representation having a lower resolution is constructed by assigning a categorical property value to each mesh of the second representation corresponding to a group of meshes of the first representation and storing parameters for changing from the second representation to the first representation with those change parameters enabling reconstitution of the first representation.