# Surface

For load geometry, two types of surfaces can be defined:

1. **Quadrilateral**: Surfaces with four sides can be defined, allowing users to input specific parameters such as start and end stations, transverse offsets, and width.
2. **Arbitrary Polygon**: Surfaces with irregular shapes can also be defined, enabling users to specify points for the desired surface geometry.

For the Steel I Girder Training Example, the quadrilateral surface definition is provided in the following section of the documentation.