# Surfaces
Types of Surfaces
Within T3RRA Design Plus, Surfaces are categorized into the following (depicted here):
- Base - denoted by no letter in the tile
- Design - denoted by the letter ‘D’ in the tile
- Overlay - denoted by the letter ‘O’ in the time
These are important to take note of as many functions with T3RRA Design Plus require certain surface types (i.e. Design surfaces are required when exporting files, creating a Cut/Fill Surface requires both a Base surface and a Design surace).
Should you need to change the category of a surface, you can do this by:
Selecting the necessary surface > Layer > Selecting either of the three options to change to the desired surface type
Surface Tools
The tools specific to surfaces fall into three main groups:
- Surface design
- Drainage
- Surface Derivatives
Surfaces are the primary layer type for work in T3RRA Design Plus, however many of the surface tools are dependent on other layer types being present. For example, the surface design tools require a boundary to be present.
These are explained in more detail in Surface Design Tools