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