A process of characterizing a process window of a patterning process, the process including: obtaining a set of inspection locations for a pattern, the pattern defining features to be applied to a substrate with a patterning process, the set of inspection locations corresponding to a set of the features, the set of features being selected from among the features according to sensitivity of the respective features to variation in one or more process characteristics of the patterning process; patterning one or more substrates under varying process characteristics of the patterning process; and determining, for each of the variations in the process characteristics, whether at least some of the set of features yielded unacceptable patterned structures on the one or more substrates at corresponding inspection locations.