# Surface \[TB] Two types of surfaces can be defined for use in load definitions: **Quadrilateral**: Surfaces with four sides can be defined, allowing users to input specific parameters such as start and end stations, transverse offsets, and width. **Arbitrary Polygon**: Surfaces with irregular shapes can also be defined, enabling users to specify points for the desired surface geometry. Refer to the following sections in the documentation for further explanation of each type. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.openbrim.org/templates/truss-bridge-workflow/loading-tb/load-geometry-definitions-tb/surface-tb.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.