Proportion

a balanced relationship of the parts to the whole. Harmony, consistency or coherency, spatial relationships.

Basic knowledge of proportion was used by Western artists was known as long ago as 300 BC when Euclid distilled the mathematical knowledge of the ancient world into a book called the Elements - he described the fixed principles behind the science of geometry. The foundation of a system of proportion is a ratio. A ratio suggests a quantitative comparison between two things. Size itself is not of prime importance. Relative dimensions or interrelationships are what matter.

See

The Golden Section - a rectangle having constancy of interrelationship and harmonic divisibility based on the human figure. (In fact Ancient Greeks used measurements of the "foot" based on an actual human foot.)

http://www.arts.rpi.edu/%7Eruiz/IMAGING/goldensec.html