Final answer:
The comparative relationship in scale of one part of a design to another in hair design is known as proportion. It is crucial for creating a balanced look that is harmonious and suits the individual's features. Hierarchical scale is a related concept where the size indicates relative importance, often used in historical artworks.
Step-by-step explanation:
The comparative relationship in scale of one thing to another in hair design is called proportion. Proportion refers to how the size of one part or feature of a design relates to other parts or to the whole design. For instance, in the context of hair design, the length of a haircut in relation to the overall shape of the client's face and head would reflect the proportion of the hairstyle. In other artistic contexts, scale and proportion can be used to create visual harmony or to emphasize certain elements. For example, the use of hierarchical scale can signify the relative importance of figures in artwork, wherein more important figures are depicted as larger than less important ones. This is a method often seen in historical artworks, such as those from ancient Egyptian civilization, where kings are depicted as larger than their subjects to convey their importance.