Special Topics in GIS - Module 2.1: Surfaces - TINs and DEMs

Hello Everyone!

This weeks lab is one of my favorite labs so far that I've done in my special topics GIS class. For this weeks lab, it was all about working with surface data. When working with surface data in GIS, there are two main types of surface data TINs (Triangular Irregular Networks) and DEMs (Digital Elevation Models). TINs are a vector-based surface data type that uses vertices distributed across the surface to draw triangular edge lines that connect these vertices together. None of these triangle surfaces overlap and you can find that they can better visualize surfaces that vary greatly compared to surfaces that have little to no variance. DEMs share some similarities with TINs, like TINs, DEMs are a great way to visualize a continuous surface. Unlike TINs, DEMs are a raster-based surface data type that uses elevation points within a series of grid cells. These cells can range anywhere from one meter to fifty meters in size. Each cell in the DEM has a unique value. Compared to TINs a digital elevation model is much smoother in showing the surface data while the DEM is much more geometric. While TINs and DEMs are different in the way they visualize surface data, there are a variety of useful functions that they can both do. You can symbolize these two types of surface data in various ways from elevation to slope and aspect values. With this surface data, you can also create contour lines. Below you can see the differences between a TIN and a DEM.

Slope Symbology (DEM)

Aspect Symbology (DEM)

Slope with Contours (TIN)

I could write pages about TINs and DEMs and all the practical and unique uses they have. Before I wrap up this weeks blog, I would like to share with you a DEM project that I worked on this past year that showcases the beauty of working with the aforementioned surface data types. 

For this project, I used a LiDAR (Light Detection and Ranging) image (Top) of the surface of Crater Lake in Oregon taken via remote sensing. Crater Lake almost fills a ~2,200 ft deep caldera that formed roughly 7,700 years ago when the volcano Mount Mazama collapsed. It is the deepest lake in the United States with a depth of 1,949 feet and ranks as the ninth deepest rank in the world. From the LiDAR image, I created a hillshade which is essentially a grayscale representation of the earth's surface in 3D that takes into account the position of the sun to shade the terrain. Once my hillshade was created, I overlayed the original LiDAR image and symbolized it by elevation (cool colors low, warm to gray colors high). I then added bathymetry data to show the depth of the lake. I hope you have enjoyed this weeks lab material, working with surface data is one of the coolest GIS applications! 

~Map On!