A method including obtaining at least a clip of a design layout, and determining a representation of the clip on a patterning device, under a condition that a reduction ratio from the representation to the clip is anisotropic. A method including obtaining a relationship between a first geometric characteristic in a design layout or an image thereof, and a second geometric characteristic in a representation of the design layout on a patterning device, wherein the relationship is a function involving reduction ratios in two different directions.