Atomic force microscope images of aluminium sheet are used to calculate the mean roughness Ra andthe root mean square roughness Rq for different directions ([theta]) across the samples. The angle determined valuesof Ra([theta] and Rq([theta]) are significantly lower in the rolling direction than in any other direction. The resultsprovide a clear demonstration of the vector nature of surface roughness. Local features in an angle determinedRq([theta]) profile are also compared with the positions of peaks and valleys in the matching topographical crosssectionof the surface running at right angles to [theta]. It is further found that the distribution of z heights for animaged sample is usually not Gaussian in shape unless the z heights are measured about mean lines constructedacross the surface parallel with the rolling direction. The results are relevant for controlling lubricationperformance in the aluminium rolling process.