Abstract: In an electron beam system in which the beam is exposed in selected prescribed patterns on a target surface, stored pattern data specifies the location of the pattern as coordinates on the target plane of a reference point in the pattern, specifies the shape of the pattern as a code identifying one of several permissible shapes, and specifies the size of the pattern as dimensions of first and second pattern dimensions in the target plane. In exposing each pattern, the data is: modified to provide the selected pattern in the desired size; modified to determine the maximum beam size for the selected pattern; dynamically fragmented into individual beam flashes; and examined to determine the beam spot size, shape and position for each flash. All patterns are generally designated as trapezoids, with a triangle considered as a trapezoid having one side of zero length, a rectangle considered as a trapezoid having four right angles, etc.