Raster and Terrain Analysis: Lab 8 Instructions Guide

1 Lab 8: Raster/Terrain Analysis _______________________________________ DUE: Thursday, November 3 rd , 5:30 pm (15 points) Answer all the questions in a Word document named Lab8_YourFirstName_YourLastName.docx and upload it together with other deliverables to Canvas (Lab 8). It is not necessary to write out the questions. Use the task number and question number from the exercise instructions to identify your written answer. This exercise consists of four tasks covering basic operations of raster data analysis: 1. In Task 1 , you will carry out a local operation, cell-by-cell using a scalar as the operator 2. In Task 2 , you will derive a slope, an aspect, and a hillshade surface from an elevation grid 3. In Task 3 , you will perform a viewshed analysis 4. Task 4 is an example of a zonal operation Remember to SAVE your ArcGIS Pro project often so that you do not lose any (or as little as possible) of your work, should the software shut down unexpectedly.

2 Task 1: Perform a local operation on a grid using a scalar In this task, you will run a local operation to convert the elevation values in plne from meters to feet. 1. Launch ArcGIS Pro and rename the map frame to Task1 2. In the catalog pane, navigate to Lab8 and add plne to the contents pane (click Yes on the pop-up asking about calculating statistics) 3. Right-click plne → Properties → Source. Examine the raster properties. Q1: How many cells are there in the raster if you would multiply the number of columns by the number of rows? (1 point) _____________________________________ Now you will learn how to display and hide NoData cells The NoData cells use “No c olor” by default. 4. Right-click plne → Symbology • Click on the Mask tab in the bottom section of the Symbology pane • Click the drop-down next to the Nodata field and select a color to display the NoData value (e.g., red) 5. Right-click on the plne grid and open the attribute table • The table shows the cell count for each elevation value • Right-click the Count column and select Statistics. It says that the total number of cells is 142,005

3 Q2: How come this number is different than the one for Q1? Hint: Look at the border of the raster… (1 point) ______________________________________________________________________________ ______________________________________________________________________________ Q3: How many cells carry a NoData value in the plne grid? (1 point) ______________________________________________________________________________ 6. Hide NoData cells by selecting “No color” for NoData cells again (i.e., go back to the Mask tab in the Symbology pane for the plne grid) You will now learn how to set the analysis environment. 7. In the ribbon, click on the Analysis tab and in the Geoprocessing group, click on Environments • In the Environments dialog box, click on the folder next to the Current Workspace and set it to your Lab8 folder. Do the same for the Scratch Workspace. Click OK. Note: The Current Workspace is the default input directory. The Scratch Workspace is the default directory for output datasets. You will now convert the elevation values from meters to feet! 8. In the ribbon, click on the Analysis tab and in the Geoprocessing group, click on Tools • Search for Raster Calculator and select the Raster Calculator (Spatial Analyst Tools)

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4 • Enter the following formula in the Map Algebra expression box: "plne" * 3.28 • Save the Output raster as plne_feet and click Run The new raster, called plne_feet show the elevation in feet instead of meters as the original grid. You will notice the default output directory is your Lab8 folder now and not the lab8 geodatabase that is automatically created when you set up a project. Meaning, you do not have to select output directory again and again. Also note that when no file extension is used for the output raster, the output raster will be in GRID format. If you use an extension, the output raster will be saved in the format you specify. E.g., if you save the output as plne_feet.tif , the output raster will be a TIFF file. Furthermore, your output raster plne_feet , unlike the original raster, will be a floating point raster. This is because we multiplied the integer raster plne by 3.28, which is a floating point number. As a result, the output raster will use this higher-level number type by default. You will now extract the areas in plne_feet which has an elevation above 3,000 feet. 9. Go back to the Raster Calculator, enter: "plne_feet" >= 3000 10. Save the raster as plne_3000 The cells with a value of 1 in the output raster plne_3000 (see image below) meet the specified criterion. Therefore, we can count the number of cells with value 1 in plne_3000 and subsequently calculate the total area of as plne above 3,000 feet.

5 11. Open the attribute table of plne_3000. The number of cells with elevation above 3,00 feet is 72,953. 12. Go to the Properties of the plne_3000 grid and look up the cell size (under Source → Raster Information). The cell size is still given in meters as in the original plne grid even if we have converted the elevation to feet in the plne_feet and plne_3000 grids. Given the cell size of 30x30 meters, we get that each cell is 900 m 2 . Therefore, the total area of plne above 3000 feet is 72953 x 900 = 65,657,700 m 2 . Q4: What area of plne has elevation between 4,000 feet and 5,000 feet (including 4,000 and 5,000 feet)? Include units of measurement. (1 point) ___________________________________ Hint: You will need to use an AND (or &) operator in the Map Algebra expression to retrieve cells with elevation values greater or equal to 4000 feet and less than or equal to 5000 feet. You will also need to put parentheses around each logical statement. For example, to find cells with values greater than 2 and less than 5 in the grid rasterinput we would need to use the syntax: ("rasterinput" > 2) & ("rasterinput" < 5)

6 Task 2: Create slope, aspect, and hillshade surfaces from an elevation grid 1. Insert a new Map frame, rename it Task2, and add plne to the Contents pane 2. First you will create a slope map of plne using the Slope tool • In the Geoprocessing pane, search for Slope and click on the Slope (Spatial Analyst Tools) 3. Use plne as your Input raster, save it as plne_slope and leave the other options to their default values 4. Create an aspect map of plne by using the tool Aspect (Spatial Analyst Tools)

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7 5. Create a hillshade map of plne by using the tool Hillshade (Spatial Analyst Tools) • Check the Model shadows option 6. Create an aspect-slope map of plne by using the Aspect-Slope raster function • In the Contents pane, select the plne layer • In the ribbon, click the Imagery tab and click the Raster Functions icon and then select Raster Functions in the drop-down • In the Raster Functions pane, scroll down to Surface and select Aspect-Slope • Set Raster to the plne layer and click Create new layer

8 Read over the Help website for the Aspect-Slope function (which can be found here ) and address the following questions. Q5: Explain how we can identify valley and ridges using the aspect-slope map. (1.5 points) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q6: When would you use an aspect map? Consult this week’s readings and lecture slides . (1.5 points) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________

9 Task 3: Perform viewshed analysis For this exercise, you will need the plne elevation grid and lookout.shp , a lookout location shapefile, both contained in your Lab8 folder. The lookout location shapefile contains two points, labeled 1 and 2. A viewshed analysis can determine areas in plne that are visible from the two lookout locations as well as areas that are not visible. 1. In ArcGIS Pro, insert a new Map frame and rename it Task3 2. Add plne and lookouts.shp to the Contents pane (make sure lookout are on top of plne in the Drawing Order). You may also want to change the symbology of lookout to make it display better like in the image below. 3. In the Geoprocessing pane, search for Viewshed and select Viewshed (Spatial Analyst Tools) • Use plne as your Input raster, lookout as your Input point or polyline observer features • Save your Output raster as viewshed (see image below) • Click Run

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10 The result should look like this.

11 Viewshed separates the visible areas from non-visible areas. Portions of the visible area are only visible to one observer point, while others are visible to both observer points. 4. First, add the plne_hillshd grid that you created in Task 2 to the map. Place it right under viewshed in the Drawing Order in the Contents pane. We are doing this to give our final map a more informative look. 5. Right-click viewshed and select Symbology • In the first drop-down in the Symbology pane, select Unique Values 6. Under Raster Layer in the ribbon, in the Effects group, set the Transparency to 50% The viewshed layer now shows three classes in 50% transparency (see image above). 7. Open the attribute table of viewshed. The table shows cell counts for the three classes: • 0 – not visible • 1 – visible from one observer point • 2 – visible from both observer points Q7: What is the total area of cells that are visible from both observer points? Include units of measurement. (1 point) _______________________________________________________ To learn more about the Viewshed tool in ArcGIS Pro, visit the tool reference here .

12 Task 4: Perform a zonal operation In this task, you are asked to derive annual precipitation statistics by watershed. Both layers are projected onto the same coordinate system with the linear unit set to meters. The precipitation measurement unit is 1/100 of an inch; for example, a cell value of 675 means 6.75 inches. 1. In ArcGIS Pro, insert a new map frame, rename it Task4, and add precipgd and hucgd to the Contents pane (click Yes in the calculating statistics pop-ups) • precipgd is a raster showing the average annual precipitation in Idaho (recorded in the VALUE field) • hucgd is a watershed raster (here the VALUE field is the watershed ID) 2. In the Geoprocessing pane, search for zonal statistics . Select the tool Zonal Statistics as Table (Spatial Analyst Tools) 3. Select hucgd as the Input Raster or Feature Zone Data, VALUE for the Zone Field, precipgd as the Input Value Raster, and save the Output Table as precip_huc • Leave the Ignore NoData in Calculations box checked and let all other parameters be set to their defaults • Click Run • The precip_huc table will show up under Standalone Tables in the Contents pane after the tool is done running 4. Now, join the precip_huc table to the hucgd raster. Use the VALUE field (this is the Zone Field/watershed ID) in both layers as the key/Input Join Field.

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13 5. Open the attribute table of the hucgd raster. The VALUE field is the watershed ID and the MIN, MAX, RANGE, MEAN, etc. is the precipitation statistics for each watershed. Q8: Which huc zone (use the OID) has the largest mean annual precipitation? (1 point) _______ Task4\Map: Change the symbology of the hucgd raster so that all watersheds except the one with the largest mean annual precipitation have the same color. Give a different color to the one with the highest mean annual precipitation. Make a map of your result that includes your name, date, north arrow, scale bar, title, and legend. Make sure the legend can tell the reader which color is the largest mean annual precipitation. (6 points) Rubric Task Description Points Task 4 Task4\SS1 Map showing watershed with largest mean annual precipitation in one color and all other watersheds in another color. Map includes name, date, north arrow, scale bar, title, and legend. Legend clearly shows the reader which color is the largest mean annual precipitation. 6 Questions throughout 8 questions Answered all questions completely and correctly. 9

Lab8_instructions

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