1. A computer-implemented method for providing a spatial map of defects in at least a portion of a mask pattern, comprising: receiving the mask pattern for use in a photolithographic process; using the computer, calculating a simulated wafer pattern based on a model of a photoresist used in the photolithographic process, the calculated simulated wafer pattern produced at an image plane in the photolithographic process when at least the portion of the mask pattern, illuminated by an associated source pattern, is at an object plane in the photolithographic process; determining the defects in at least the portion of the mask pattern based on differences between the calculated simulated wafer pattern and a target pattern, wherein the target pattern excludes the defects; and providing an image of a spatial map for presentation in a graphical user interface associated with a mask-pattern analysis software, the spatial map visually representing the determined defects in at least the portion of the mask pattern.