1. A method of quantifying how well a photolithographic model simulates a photolithographic printing process, comprising: receiving a number of simulated features produced by a model that simulates how a test pattern will print on a wafer with a photolithographic process, the simulated features comprising one or more edge segments; receiving a description of the shapes of printed features on a wafer printed using the test pattern; and using a computer, comparing the shapes of the simulated features with the shapes of the printed features by calculating one or more distances between at least one point on one of the printed features and at least one of the edge segments to quantify how the photolithographic model simulates the photolithographic printing process.