Unity is a relation of all the parts or elements of a work constituting a harmonious whole and producing a single general effect.

Asymmetric Balance not exact but counterbalanced with contrasts such as dull and bright colors, dark with light values, geometric with organic shapes, active and inactive areas and its first cousin below

Symmetric Balance exact of even balance along a centerline or "axis" in these ways:

Radial Symmetry rotating around a center point, Exact Symmetry a mirror image or an exactly repeated design, Axial Symmetry having 2 opposing repeats, one on each side of an axis.

Scale in drawing refers to the proportion or ratio that defines the size relationships.  Models, architectural plans, maps and paintings/drawings all use scale to create the illusion of correct size relationships between objects and figures. 

A hierarchy of genres is any formalization which ranks different types of genres in an art-form in terms of their value.