1. A method, performed on a computer system, for determining a localized measure of regional pattern density in a fabrication process of a chip, the method comprising: using the computer system to perform the following: determining pattern density values for each cell of a plurality of cells of interest; averaging the pattern density values for each cell within a first selected region about and including a target cell to determine the localized measure of regional pattern density for the target cell, wherein the averaging includes using pattern density values from a diametrically opposite side of the chin to complete the first selected region when the first selected region about a target cell extends beyond a border of the chip; storing the localized measure of regional pattern density for the target cell; and repeating the averaging and the storing for each of the plurality of cells.