1. A method for generating a pattern of a mask to be used for a mask manufacturing method for manufacturing the mask using data of the generated pattern of the mask for an exposure apparatus that exposes a substrate with light by using a projection optical system that projects an image of the pattern of the mask on the substrate, the method comprising the steps executed by a processor of: applying, to a target main pattern, a reference map of a characteristic value of an image of a representative main pattern with respect to a position of a representative auxiliary pattern and calculating a map of the characteristic value of the image of the target main pattern with respect to a position of an auxiliary pattern; and determining the position of the auxiliary pattern by using data of the map of the characteristic value of the image of the target main pattern and generating a pattern of a mask including the target main pattern and the determined auxiliary pattern, wherein the auxiliary pattern is for the main pattern and is not resolved, wherein the characteristic value of the reference map at any one position is a characteristic value of an image of the representative main pattern projected on an image plane when the representative auxiliary pattern arranged at the one position and the representative main pattern exist on an object plane, and the reference map has the characteristic values of the image of the representative main pattern, the characteristic values being obtained while a position of the representative auxiliary pattern is changed around the representative main pattern on the object plane, and wherein the mask manufacturing method comprises a step of manufacturing the mask including the generated pattern using data of the generated pattern.