TGC is the extension given to files generated and used by a software tool called Terragen which is a digital scenery generator. The TGC file contains data that can be elements of scenes created in the program. These can be effects on the surface or layout of the terrain. Such clips can be inserted into the actual project.

Terragen is a program developed by Planetside Software that allows you to render and animate in a very realistic way, e.g. natural environments.