(TIN) GIS a representation of a surface derived from irregularly spaced sample points and breakline features —note 1. the TIN data set includes topological relationships between points and their proximal triangles; each sample point has an x,y coordinate and a surface or z value; these points are connected by edges to form a set of nonoverlapping triangles that can be used to represent the surface —note 2. TINs are also called irregular triangular mesh or irregular triangular surface modelsThis definition last updated 10/10/2008