What is the term for the similarity of form on either side of a dividing line?

The term that describes the similarity of form on either side of a dividing line is known as symmetry. Symmetry refers to a balanced and proportional arrangement of elements, where one side mirrors the other. In visual art, architecture, and nature, symmetry creates a sense of harmony and balance. When an object or shape can be divided into two identical parts that are facing opposite directions, it exemplifies symmetry.

For example, if you were to draw a line down the middle of a perfectly shaped butterfly, each side would look the same, highlighting the concept of symmetry. This principle is foundational in various fields, including mathematics, where geometric figures exhibit symmetric properties in their designs.

In contrast, asymmetry denotes a lack of balance or symmetry, where the two sides do not match. Reflection might refer to flipping an object across a line, but it doesn't inherently imply symmetry in form. Proportion relates to the size relationship between parts of a whole, but it does not necessarily address the concept of balanced similarity as symmetry does. Hence, symmetry is the term that accurately captures the idea of similar forms on either side of a dividing line.