A method for determining a training pattern in a layout patterning process. The method includes generating a plurality of features from patterns in a pattern set; grouping the patterns in the pattern set into individual groups based on similarities in the plurality of generated features; and selecting representative patterns from the individual groups to determine the training pattern. In some embodiments, the method is a method for training a machine learning model in a layout patterning process. The method may include, for example, providing representative patterns from the individual groups to the machine learning model to train the machine learning model to predict a continuous transmission mask (CTM) map for optical proximity correction (OPC) in the layout patterning process.