1. A method, comprising exposing patterns on a wafer to radiation and predicting a critical dimension map of the patterns exposed on a wafer by a scanner which generates signals during the exposure of the patterns on the wafer, the critical dimension map being predicted from the signals generated by the scanner during exposure of the patterns on the wafer, wherein the critical dimension map is predicted in situ with respect to the scanner, and further comprising creating a dose map and a defocus map, wherein the critical dimension map is predicted using the dose map and the defocus map.