Digital Elevation Models (DEMs)

The goal of this lab was to look at different DEMs, learn how to represent them in ArcMap and then present them in a creative and informative way.

First, I had to choose an area that I wanted to look at, preferably somewhere mountainous or with interesting geological features. I settled on Little Cottonwood Canyon outside of Salt Lake City, Utah. Up Little Cottonwood Canyon there are multiple ski resorts, great hiking and mountain biking, as well as some rivers and lakes. Then I had to download the data, using the same area, I wanted to compare LiDAR, autocorrelation and interpolation DEMs. To retrieve the LiDAR and autocorrelation DEMs I went to the Utah GIS website and utilized their resources. They allow you to download raster 'tiles' with the elevation information for that area. I ended up needing two tiles of both the LiDAR and autocorrelation. These had to be stitched together using the 'Mosaic to New Raster tool', which (with the correct properties entered (pixel type, cell size, etc.) will stich together feature layers with adjacent features, seamlessly.

For the interpolation DEM, I downloaded it from the USGS National Elevation Database (NED) as a .tif and added it into my map as well. When adding DEMs, much like adding anything else to your map, you HAVE to check your coordinate system. My LiDAR and autocorrelation files had no coordinate system information saved within them so I had to use 'Define Projection' to set that to the correct coordinate system (NAD 1983 UTM Zone 12N). As for the interpolation data from the NED, I had to use the 'Project Raster' tool to project it into the correct projection. When projecting rasters, you can make a big mistake by not choosing the proper sampling technique. For continuous data you have to use cubic or bilinear. The other option, nearest neighbor, will take the averages of the cells around it and you wind up with a very smooth looking mountain range.

After getting the data into the map, I created a hillshade for each one to really bring out the differences in elevation. I layered the correct DEM on each hillshade and turned down their transparency to let the hillshade shine through. To make comparisons easier, I chose the same extent and color ramp for each DEM. This ensured that they were all the same size with the proper amount of zoom on the same area. The same coloring helps to make the maps more pleasing but also easier to discern to differences in accuracy of elevation between them.

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Sources:

National Elevation Database-USGS

Utah AGRC

"Digital Elevation Models—Related Concepts | Documentation". Learn.Arcgis.Com, https://learn.arcgis.com/en/related-concepts/digital-elevation-models.htm.