This is a subclass for the description of triangular irregular networks. The triangles needed to define the TIN are provided. If the TIN is based on a specific set of surface defining features these may be provided by as a textual description by the attribute surfaceDefining. The method states the algorithm or scheme used to create the triangulation. The usual method is Delaunay triangulation; however, where the terrain has preferred directions, other techniques may result in a TIN which better approximates the surface.