A sectional drawing provides a view of an object as though it had been cut along some imagnary plane. A scenic sectional, also called a hanging plot , shows a sectional view of the stage with the cutting plane of the section being on the center line of the stage. this drawing is used to show the relative position of the act, masking, and various lighting instruments. it is used to help determine trim heights for masking , the heights of various scenic pieces , and similar tasks. a sectional drawing frequently provides the best way of explaining a shape with irregular surfaces, as shown in figure 7.22B.
  Other sectional drawings are used for variety of purposes. the vertical and horizontal sectional drawings that are used for determining sight-line drawings are discuss in chapter 8, perspective drawing, and the sectional drawings used in lighting design are discuss in chapter 14," lighting design''.

oh sorry.
i will post again the types of sectional drawings
There are three major types of sectional drawings:
full section, half section, part section
they are full secction, half section and part section