To solve the problem that there is a case in which plotting fraudulence may be occurred, and that this may be different from the plotting result intended by a user by thinning out coordinate points.

This data processor is provided with a means for extracting the coordinates of the vertexes of the outline of a plurality of rectangular areas brought into contact with each other according to an image formation request for designating painting or clipping in a plurality of rectangular areas brought into contact with each other; a means for thinning out a portion of the extracted coordinates of the vertexes of the outline according to device resolution; a determination means for determining whether to perform the thinning processing according to the changing quantity of the coordinates of the vertexes of the outline; and a means for generating print instruction data to designate the designated painting or clipping from the coordinate dot sequence of the vertexes of the outline after thinning out.