# Definition:Symmetry Mapping

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## Definition

A **symmetry mapping** (or just **symmetry**) of a geometric figure is a bijection from the figure to itself which preserves the distance between points.

In other words, it is a self-congruence.

Intuitively and informally, a **symmetry** is a movement of the figure so that it looks exactly the same after it has been moved.

## Examples

### Rotations of Square through $90 \degrees$

Let $S$ be a square embedded in the plane centered at the origin $O$.

A rotation of the plane through an angle of $90 \degrees$ either clockwise or anticlockwise is a symmetry mapping of $S$.

## Also see

- Results about
**symmetry mappings**can be found here.

## Linguistic Note

The word **symmetry** comes from Greek **συμμετρεῖν** (**symmetría**) meaning **measure together**.

## Sources

- 1965: Seth Warner:
*Modern Algebra*... (previous) ... (next): Chapter $\text I$: Algebraic Structures: $\S 2$: Compositions: Example $2.5$ - 1971: Allan Clark:
*Elements of Abstract Algebra*... (previous) ... (next): Chapter $2$: The Definition of Group Structure: $\S 26 \eta$ - 1978: Thomas A. Whitelaw:
*An Introduction to Abstract Algebra*... (previous) ... (next): $\S 34$. Examples of groups: $(5)$ - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**symmetry**(of a geometric figure)