An apparatus and method of synthesizing a photolithographic data set includes using a first computational model to calculate a first figure-of-merit for the photolithographic data set; changing a first part of the photolithographic data set to increase the first figure-of-merit; and then using a second computational model to calculate a second figure-of-merit of the photolithographic data set; and changing a second part of the photolithographic data set to increase the second figure-of-merit. The second computational model enables figure-of-merit calculations to be executed at a significantly faster execution rate than the first computational model.