The TIN model represents a surface as a set of contiguous, non-overlapping triangles. Within each triangle the surface is represented by a plane. The triangles are made from a set of points called mass points. Mass points can occur at any location, the more carefully selected, the more accurate the model of the surface. The TIN model is attractive because of its simplicity and economy and is a significant alternative to the regular raster of the GRID model.
Contours are a common source of digital elevation data .
In general all the vertices of the contour lines are used as mass points for triangulation. In many cases this will cause the presence of flat triangles in the surface. Flat triangles are frequently generated along contours when the sample points occur along the contour at a distance that is less than the distance between contours. The flat triangles have a slope of 0 and do not have defined aspect. They might cause problems when the surface is used for modeling.