Lab 7 - Surfaces: TINs and DEMs

This module was really neat! As the title suggests, we examined two terrain models: TINs (Triangular Irregular Networks) and DEMs (Digital Elevation Models). Terrain (elevation) models are very popular in GIS applications; from watershed delineation to visibility analysis, you can expect to use elevation models at one point or another in your GIS career. So which one is better? What is the difference?

In our lab assignment, we compared both elevation models by creating 3D visualizations in ArcScene (through the 3D Analyst Extension), by using various Spatial Analyst Extension tools, and by using ArcMap through a series of exercises.

DEMs are raster-based models, while TINs are vector-based. What's really unique about TINs is that they are triangular! The nodes that make up the vertices of the triangles are created from point elevation data, and then connected using edges to form a network of triangles. Because of this creation method, TINs tend to create really sharp, jagged contour lines and surfaces (as pictured above). DEMs on the other hand are smooth, continuous, and provide natural-like curvature for geographic features such as streams and lakes. In addition, DEMs are more readily available for download and as free resources, while TINs aren't and are most costly. DEMs also cover larger areas, while TINs cover smaller areas; TINs do have a one-up on this as the accuracy of data is higher.

One of my favorite differences between TINs and DEMs are their visualization capacities through 3D Analyst/ArcScene and ArcMap. With a TIN, it can automatically be brought into ArcScene as a 3D image without needing to drape it over an elevation, as you would with a DEM. Additionally, with a TIN, we can inspect Elevation, Slope, and Aspect from the same TIN layer. All of the features in the picture above can be placed on top of one another from the same TIN layer in both ArcMap and ArcScene. This cannot be said the same for a DEM, as each requires separate grids that must undergo a geoprocessing tool.