# Derived Entities

*Derived entities in Flow360 are entities that are created based on input geometry. These entities serve specific purposes in simulation setup, such as assigning symmetry in the model.*

## Farfield

*Farfield entities define the outer boundaries of your computational domain. They are automatically generated based on your geometry and control the extent of the flow field simulation.*

## Symmetry

*Symmetry entities are used to reduce computational domain size by utilizing geometric and flow symmetries. They allow you to simulate only a portion of the full domain when the flow physics and geometry exhibit symmetrical properties.*

Symmetry planes are automatically created when using Farfield based on chosen method:
- `Auto`, a single symmetry plane named "symmetric" is created when using semi-spheres
- `Quasi-3D`, two symmetry planes named "symmetric-1" and "symmetric-2" are created on both sides of the thin disk