NOTE: you may need to activate the Spatial Analyst extension to access some of the tools needed for this lab.
In ArcMap go to the Customize drop down > Extensions. Click in the Spatial Analyst box to toggle on the check mark > Close. (You can go ahead and turn on any other extensions you want at the same time.)
These instructions DO NOT walk through every step of that process for you. However they do cover most of the tricky parts once (i.e. for one of the four resolution DEMs) and then we expect you to be able to apply that knowledge by doing the same thing for the other datasets. We start our instructions focusing on finding where our study site is, and then we start with the high resolution data first (2m LiDaR DEM) and move on to the easier coarser resolution datasets. As with all the instructions in these labs, this is not the only way to do things, but it is suggested
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LiDAR2006_2m_BareEarth_Tiles from the 2m LiDaR page, and performed a Select by Location to find the tiles in the LiDAR2006_2m_BareEarth_Tiles attribute table that were within the Big Cottonwood Canyon Watershed:
Now we have a problem. When we look at the LiDAR2006_2m_BareEarth_Tiles attribute table, we see the query has correctly returned 51 records (note you can view just the selected in the attribute table with the Show Selected Records button:
The problem is that it would take a VERY long time to download all 51 tiles individually, then load them up, perhaps combine them into one very large raster layer (e.g. using the mosaic command). If at the end of lab you're feeling particularly ambitious and have extra time, feel free to undertake such a brute force exercise for extra credit. However, for the rest of us, this is a perfect example of where we may want to make an executive decision to limit our download and processing time up front, and instead, create an detailed visual comparison using a subset of the LiDAR data, and make a compelling case to the client detailing the pros and cons of using high resolution lidar data.
To figure out these tiles, I zoomed into the area around Solitude (easy to spot from aerial imagery basemap layer if you've been there, but also easy to confuse with Brighton). The video shows you how to choose the tiles.
The LiDaR tiles we want from Utah AGRC are
One of the annoying things about how Utah AGRC is providing these LiDaR tiles is that they are in an Arc ASCII grid format. The format is convenient for being able to read the file in a text editor and/or other programs, but is not at all convenient for straight import into ArcGIS. The Arc ASCII grid also has no projection associated with it. You will notice that on the Utah AGRC download page they have provided instructions for Using ASCII Files in ArcMap. They tell you the projection and datum you should use and how to add these files to their own geodatabase. I suggest you follow those instructions (excerpt below):
'The File-based Geodatabase is great for working with elevation data. In ArcCatalog right mouse click in the location you want to create your database and select New->File Geodatabase. Next right mouse click the database and select New->Raster Dataset. The Pixel Type should be set to 32_BIT_FLOAT and the Spatial Reference set to NAD83 UTM Zone12 North for the XY Coordinate System and a North America NAVD1988.prj for the Z Coordinate System. With your new Raster Dataset, Right mouse click and select Load->Load Data. Select the
There are multiple places in the simple step of converting and loading the ASCII raster DEMs into a more useful form in ArcGIS that folks get confused and get derailed. As ASCII raster data is such a common form in which DEMs and other raster datasets are made available, these are essential skills to develop and understand each step. The video tutorial provides you with a little extra explanation and step-by-step explanation of the steps described in the Using ASCII Files in ArcMap instructions from the Utah AGRC.
Note, you will find these rasters display quicker if you Build Pyramids for them (right click on the raster dataset to access this command).
Note: If this process doesn't work, Run the ASCII to Raster tool (Conversion) - saving the ascii files as *.TIF files, then the Mosaic to New Raster tool which will combine the two new TIF rasters. Make sure you set the XY and Z coordinate systems for the New Raster in this second step. Don't include a file extension. Pixel type and Bands should match the input rasters (check the properties).
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Auto_Correlated_DEM_5m from the 5 Meter Auto-Correlated Elevation Model (DEM) page on the Utah AGRC. Using a similar select by location to find the tiles in the Auto_Correlated_DEM_5m attribute table that were within the Big Cottonwood Canyon Watershed. You should find that there are four tiles you will need (this is better then 50+ tiles, get them all):
interactive download map, the tiles that intersect the Big Cottonwood Canyon Watershed are those highlighted in orange above.
You will notice that like the LiDaR rasters you download, these are also Arc ASCII Raster (
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National Elevation Dataset from the US Geological survey and are derived from the contour data used to make the 7.5" USGS Topographic Maps we worked with in Lab 3 and an earlier quiz. We will download these datasets from Utah AGRC because they have organized this by county (fortunately our entire watershed falls within Salt Lake County) and because they provide these in Arc Raster Grid formats that include pyramids, projections, and metadata. Use:
For task 1, you've been asked to make figures comparing each of these four DEMs at the full watershed scale. In order to make these graphically pleasing and to use consistent symbology between the DEMs, we need to learn how to use Hillshades and manipulate the symbology and display properties, applying the same color ramps to the different rasters. This video covers those basics with a comparison between two of the four data sets:
If you find that you are having trouble getting the 2m LiDaR to have a comparable color ramp to the three other DEMs, you may find this video tutorial helpful:
Finally, your Boss's instructions do not provide specific guidance as to how to display your DEMs. He did say he wants them just for the watershed, but you may decide that you want to show the DEM for the watershed as well as part of the DEM outside your watershed (for context). This is exactly what the Salt Lake City Public Utilities Department did in the map below:
There is no single correct way to make your maps for Task 1 and we will leave that up to your creativity and professional judgment. You may find that either implementing a display clip (of a data frame) or a physical clip of the raster dataset to the watershed boundary are extremely useful tools to have at your disposal. This video tutorial goes through an example of each with the 30 m DEM.
So that the Cottonwood Canyons Foundation has some eye candy, you can use ArcScene to create a 3D view of the Canyon. You can choose any of the DEMs to do this from. This video can help you through the basics:
what to submit section for Task 1.
Proceed to Task 2