In one embodiment, a data generation method is for calculating a coverage of a polygon in each of a plurality of pixels obtained by dividing a target to be irradiated with a charged particle beam into predetermined sizes. The method includes dividing a parametric curve that defines a pattern shape into a plurality of parametric curves, calculating, for each of the plurality of parametric curves, an area of a region surrounded by a segment connecting end points among control points of the parametric curve and the parametric curve, calculating positions of vertexes of a figure having an area equivalent to the calculated area and having, as one side thereof, the segment connecting the end points, and generating the polygon by using the vertexes.