"Composition is the two-dimensional arrangement of the drawing elements on the paper. The paper itself establishes a format, and it is the relationship of all the drawing elements to this format that creates the composition.
Originally, drawing textbooks set out rules concerning composition. These were established and adhered to for the sake of harmony, balance, and proportion. Classic compositions were generally stable; romantic compositions more unstable...
Breaking the rules of traditional composition has led toward greater expressiveness in drawing. The compositional rules that generated harmony have been broken in favor of expressions of tension, weight, and imbalance. Composition as harmony has been replaced by composition as expression."
-from Diane Douglas and Dirk van Wyk, The Drawing Process (Englewood Cliffs, NJ: Prentice-Hall, Inc.), 1993.