1. A method of producing a dataset for creating a photomask set used in patterning a target layout of line features and large features in a circuit design, comprising: receiving a layout dataset representing features of the circuit design; deriving a first dataset representing line features within the layout dataset; deriving a second dataset representing large features within the layout dataset; generating, by a computer system, a first mask dataset from the first dataset, wherein the first mask dataset represents a first pattern comprising a first array of line features, the first array of line features defining a second array of line features when subsequent to a spacer-etch process spacer material remains adjacent vertical surfaces of the first array of lines, thereby forming the second array; generating, by a computer system, a second mask dataset from the first dataset, wherein the second mask dataset represents portions of the second array of line features to be selectively removed, thereby forming the line features of the target layout; and generating, by a computer system, a third mask dataset from the second dataset, wherein the third mask dataset represents a second pattern comprising the large features of the target layout.