A method of forming a pattern includes defining a plurality of patterns, defining a plurality of pitch violating patterns that contact the plurality of patterns and correspond to regions between the patterns, classifying the plurality of pitch violating patterns into a first region and a second region that is adjacent to the first region, selecting one of the first region and the second region, and forming an initial pattern defined as the selected first or second region. The selecting includes performing at least one of i) selecting a region that contact dummy patterns, ii) selecting a region of a same kind as one region, and iii) selecting a region that contacts a concave part of an enclosure from the first region and the second region.