Examples for correlations of results of Scanning Tunnelling Microscopy (STM) with thickness dependent physical properties of thin films will be discussed: surface roughness enhances the thickness dependent resistivity. This effect can be described quantitatively by STM imaging. Good agreement with a simple model of the film resistivity can be found for Au and Cr-Au films. The magnetization loops of Au-Fe-Au films depend on the preparation parameters, although RHEED indicates identical flat surfaces. STM, however, often shows different local topographies. Again a direct correlation can be established.