1. A method comprising: receiving a first mask pattern, at least a portion of the first mask pattern having a first mask feature; synthesizing a first near-field corresponding to said at least a portion of the first mask pattern using a library of corrections; generating a second mask pattern by modifying the first mask pattern, said modifying the first mask pattern comprising modifying the first mask feature; determining a first effect on the first near-field corresponding to said modifying the first mask feature; synthesizing a second near-field corresponding to at least a portion of the second mask pattern by applying the first effect to the first near-field; using said second near-field to determine a second wafer pattern corresponding to said at least a portion of the second mask pattern; and comparing the second wafer pattern to a desired wafer pattern.