1. A computer-readable medium containing a number of instructions that are executable by a processor to create mask data by: reading all or a portion of a desired layout design that defines a number of features to be created on a semiconductor wafer; defining data for bridge structures that connect the features to be created on the semiconductor wafer; and analyzing the data for the features and the bridge structures in order to assign phase values to the data that define the features such that the features on opposite ends of each bridge structure are assigned different phase values, wherein the mask data includes the data for the features with the assigned phase values but omits the data for the bridge structures.