Effect of beam convolution in the presence of intensity gradients on the radial sampling of the rotation velocity. Left panel: deviation of the sampled radius (i.e. the radius within the beam at which the intensity and therefore the weighting of the velocity is highest due to the convolution with the beam) from the real radius in the presence of smooth intensity profiles with different power-law indices. The effect is stronger for steeper intensity profiles. Right panels: effect of beam convolution in the presence of a gap-shaped intensity profile with varying depths (upper right) on the resulting residual rotation curve (bottom right). In both cases, a beam size of 76 mas is assumed, shown by the horizontal black bar.