A piece of art will have certain things placed in these spots to make it work. You can have the concept down and the idea but still need structure in the background. This helps to tie in all the pieces together instead of just hitting and missing. Sometimes just an object is needed to put it all into perspective.You can also create this with a piece of string attached to a sharp pencil on paper and rulers or even compasses. Consequently, you can turn it in many directions depending on the size of picture. Again, these examples give us an idea about how this is supposed to work.