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By modifying the rules in the representation of observations, one does not only modify the representation’s aspect, but also its informational contents, and the principles of interpreting the observations. Fourier’s filterings, associated to the use of a colour graphic variable according to its frequential physical logic, offer an alternative to the mass analysis and representation of geographical forms. After having briefly reminded the method, the author examines the changes of the concepts introduced by the space-frequency structuring of the observations. The complex surfaces are differentiated and reorganised according to the produced scale hierarchies : the links between the units and the spatial frame structuring the forms are thus highlighted. In the example proposed here, a Spot urban image, only a part of the extracted space-frequency information is presented : the value saturation/interferences, reproducible in black and white.