A known pattern area (of known shapes) is aligned with a first area of an IC design (by overlaying and centering the known pattern area on the first area). The first area is compared to the known pattern area to identify dissimilarities between shapes in the first area and the known shapes in the known pattern area as unweighted shapes. The unweighted shapes are weighted (based on the location of the unweighted shapes relative to a weighting zone pattern) to produce weighted shapes; and a dissimilarity measure between the first area and the known pattern area is calculated by summing the weighted shapes. A determination of whether the first area matches the known pattern area is made (based on whether the dissimilarity measure exceeds a threshold) and the same is output.