A processing method includes processing a wafer based on initial data, measuring errors for each of the plurality of areas, calculating an error similarity of at least some of the plurality of areas as a function of a separation distance between each pair of some of the areas, selecting a first area and a plurality of second areas adjacent to the first area, calculating weight values for the second areas based on the error similarities between each pair of second areas and the error similarities between the first area and each second area, calculating an estimated error of the first area based on the measured errors of the second areas and the weight values for the second areas, and generating estimated data based on the estimated errors for each of the plurality of areas.