1

GIS LAB 7 The Geodatabase Working with Spatial Analyst. Calculating Elevation and Slope Values for Forested Roads, Streams, and Stands. This lab will ask you to work with the Spatial Analyst extension. The data for this lab come from McDonald Forest and will build upon data we worked with earlier. We will be working with spatial data from the shapefiles we manipulated in Lab 6: forest boundary, streams, roads, and stands. One new spatial data layer we will work with is elevation from McDonald Forest. Open the Windows Explorer and navigate to the t:\teach\classes\fe257\gislab7 location on the forestry network. Using the mouse, right click on this folder and choose copy from the menu that appears. Use Explorer to navigate to your workspace folder. For most of you this will be located on the n:\drive and the will have the same name as your user name- for me it’s n:\wingm. Right click on your workspace folder and choose paste from the menu that appears. This should copy the gislab7 folder and all the data files located under it into your workspace. IMPORTING RASTER FILES The DEM we will be working with today is from McDonald Forest. It contains elevation values for the forest at a 10m per side raster resolution. Our DEM is in an ArcInfo GRID format. The ArcToolbox will import and read ArcInfo GRIDs in the same way that it reads ArcInfo export files. ArcInfo export files are a safe and popular method of making spatial data available. Export files, whether they are coverages or GRIDS, will have an .e00 suffix attached to them. In the case of large files, there may be more than one export file (an additional export file would feature an .e01 suffix) but this is rare. Measurement units within the layers you will work with are U.S. survey feet. Start ArcMap, accept the invitation to start with a New Empty Map Save your map document as gislab7.mxd in your gislab7 workspace. Choose the Add Data button, and establish a connection to your gislab7/mac_lamb folder. Add all the data that exist in this folder to your ArcMap session.

2

Activate the ArcToolbox and import the GRID file named “peavygrd.e00”.

1. Expand the Conversion Tools group. 2. Expand the To Coverage group. 3. Select the Import from E00 option.

Navigate to your workspace location and select Peavygrd as the Input file, write the result out to the same location with the same name.

3

After the processing is finished, add the newly created GRID to your ArcMap session.

4

Zoom to the extent of the GRID that you just added.

Creating a Geodatabase The best place to create a Geodatabase is within the ArcCatalog. Open this module by choosing the start menu and navigating to ArcGIS program group. Once the ArcCatalog opens, close your ArcMap session. This is important as we’re going to permanently delete some of the shapefiles in your workspace after we create a Geodatabase.

5

Make sure your \gislab7\mac_lamb is the active database connection- it should appear in the Location dialog box in ArcCatalog. If it isn’t, click on it in the left window pane of the ArcCatalog to make it active. Create a new database by choosing the File menu, the New command, and then select the File Geodatabase option.

6

You’ll see the new Geodatabase in the file viewer almost immediately and will be prompted for a file name. Let’s name the Geodatabase “McDonald.”

7

Converting Shapefiles to Geodatabases Right click on the boundary shapefile, choose Export, and select “To Geodatabase (multiple).”

8

This will open a dialog box that allows you to convert multiple files into Geodatabases at the same time. Use the first browse button to add the roads, stands, and streams shapefiles. Use the second browse button to direct your output to the McDonald Geodatabase you just created. Choose OK when ready.

9

Converting Rasters to Geodatabases The raster file we imported is in a different data format than the shapefiles and will need to be converted into the Geodatabase separately. Unfortunately, the functionality to right click on the raster and convert it directly does not exist presently in ArcCatalog. Open the ArcToolbox and:

1. Expand the Conversion Tools group. 2. Expand the To Geodatabase group. 3. Select the Raster to Geodatabase (multiple) tool

10

In the dialog box that opens, select peavygrd as the Input file and McDonald as the output destination. Choose OK to run the conversion.

11

Let’s delete the raster and shapefile databases from the ArcCatalog. Also, we’ll take a minute to view the contents of the McDonald Geodatabase.

12

Launch ArcMap from the ArcCatalog by using the ArcMap button. Choose gislab7.mxd from the list of available map documents. You should see that we’ve got some problems with the original layers since we’ve deleted them from the hard drive.

13

Right click on the roads layer, select the Data option, and then the Repair Data Source Option. Go into your geodatabase by double clicking on it. Then select the roads layer.

14

Name your data frame Peavy. Rename the raster peavygrd to Peavy DEM, zoom to its extent, turn off all other layers from view, and close the ArcToolbox. Save your map document.

15

Accessing the Spatial Analyst Extension The Spatial Analyst extension allows us to work with ArcInfo GRIDs and perform basic and advanced analyses. The extension comes packaged with ArcGIS provided that you have paid for the additional software. If you haven’t, you can purchase the Spatial Analyst extension at any time and add it to an ArcGIS product. Let’s activate this extension by choosing the Customize menu and selecting Extensions. You should see a dialog box appear. Click on the check box next to Spatial Analyst and choose Close.

Before we can access the Spatial Analyst tools, activate its tool bar by accessing the View menu, the Toolbars choice, and selecting the Spatial Analyst choice from among the options. Examining DEMs Similar to the way ArcMap displays shapefiles or covers, a default legend is created for us when we add a GRID to our table of contents. The GRID we’re examining (Peavy DEM) is actually a digital elevation model (DEM) with each of the raster cells being coded with an elevation value. The units being displayed in the legend are the elevation values. The units that they’re expressed

16

in is feet- you wouldn’t be able to tell what the units are by just looking at the legend and/or DEM map- you would have to look at the metadata or projection information for Peavy DEM. We can alter the symbology of the Peavy DEM by accessing its properties from the table of contents. Right click on the layer, choose properties, and select the Symbology tab.

By default, ArcMap uses a continuous (“stretched”) gray tone to represent the elevation values. By looking at the information in the Symbology tab, we can see that high elevation values are shaded lightly while low values are dark. In addition, we see the minimum and maximum elevation values. We can use the Symbology interface to alter the GRID’s display. In the Show box, choose Classified. This will allow us to split the elevation values into categories rather treating them continuously. Choose the classify button.

17

This should open the Classification dialog box, a place where we can control how categories are created. Set the number of classes to 7 and change the Method from Natural Breaks to Quantile. This should great seven categories, organized from low to high, each with an equal number of observations. One of the unique features of this dialog box is being able to look at the distribution of cell values (bottom frame of dialog box) and add a mean and standard deviations to the distribution. Choose OK to move on.

18

This should return you to the Properties dialog. From the Color Ramp dialog, choose a color scheme that you would like to see applied to your seven categories. You can get a preview by choosing Apply. When you’re satisfied with a scheme, choose the OK button.

You should see a differently colored map.

19

Creating Elevation Contours Let’s create elevation contours that approximate the 40 foot intervals used by the USGS 7.5 minute quadrangle series maps. We’ll need to access the Spatial Analyst toolbar.

From the Toolbox, click on Spatial Analyst Tools, choose Surface and then Contour.

20

The Input Surface is a reference to what data set we want to base our contours on. This should be Peavy GRID. Set the Contour interval to 40 and direct the output to your geodatabase in workspace/mac_lamb with the name contour40.

21

You should get a new layer from this process that is added to your table of contents.

Open the attribute table for the new layer and notice that an elevation value (CONTOUR) has been added for each row. Go ahead and close the table.

22

Creating a shaded relief map A shaded relief map can help define the topography of a landscape. The result approximates a three-dimensional scene. You can create one of these by choosing the Hillshade option from the Toolbox, Surface Analysis Tools, Surface menu.

23

This should open a dialog box where you can manipulate the direction and height of the illumination source. The Azimuth describes the angle, relative to the landscape, from which the landscape will be illuminated. The Altitude describes the vertical angle of the sun- a low small would approximate morning or evening times whereas a large angle would be closer to noon. The z factor allows us to exaggerate the relief effect. Let’s change the Azimuth to 220 but accept the other defaults. Direct the output raster to your geodatabase and title it hillshade and choose OK.

24

This should add a new layer to your table of contents. Your map should look similar to the one below. You may want to toggle the contour layer off to get a closer look at your landscape surface.

25

Save your map document! Examining histograms Let’s turn both of these new layers (contour lines and shaded relief) off and find out more about the Peavy GRID layer. Select the histogram button.

This should produce a bar graph that shows us how many grid cells fall into each of the classes we assigned to the Peavy GRID layer. If you click on any of the histogram bars (as long as the identity tool is active), the range of data values represented by the bar and the number of cells in the range is returned.

Our histogram tells us that we had seven elevation categories. Since we chose a quantile classification method, we should have an equal number of observations in each category. Bear in mind that if we changed the classification method, these results would change too. Close the histogram window. Let’s do some clean-up at this point. First delete the contour and shaded relief layers by right clicking on them and choosing remove. Make sure you have the right ones selected! Make sure

26

that the stands layer in your table of contents is below the streams and roads layers but sits above the Peavy DEM layer. Make the stands, streams, and roads visible. Save your map document!

Analyzing vector and raster data simultaneously One of the useful features of Spatial Analyst is its ability to work with vector data and GRIDs in the same analysis. The roads, streams, and stands layers are all vector files but we can extract information from the Peavy DEM layer that relates to these vector layers. Let’s find out what the average elevation of the stand units in this area are. Choose Zonal Statistics as Table from the Toolbox, Spatial Analyst Tools, Zonal group.

27

Choose Stands as the Zone dataset. We need to pick a variable from the Stands attribute table that uniquely identifies each stand unit: STANDID. Make this selection for the Zone field. By default, Peavy DEM should be the Value raster but make a change if something else is selected in your project. Finally, direct the output to your geodatabase, name the output “standelev”, and choose OK.

28

Our operation above told the Spatial Analyst to look at each of the polygons in the Stands layer as identified by the field STANDID. If two polygons shared the same attribute for this field, they would be treated as a single polygon or zone. The values from the GRID in the Value raster field will be summarized for each of the polygons or zones that GRID raster cells overlap. The histogram will be too overwhelming for us to draw much information from since all stands are represented- close this window. The next window should be more helpful.

29

The script at the bottom of the window tells us that we have 130 records represented. The first column gives us the STANDID number or unique stand unit identifier. Subsequent columns relate how many grid cells per stand unit, the area of the unit in square feet, and some summary statistics of elevation ranges for each unit. For example, we know that stand unit 040201 (the second stand record in the display above) averages 465 feet in elevation. After you’re done browsing through this table, close it. Calculating and analyzing slope We can also use the Spatial Analyst to create a slope surface from a DEM. Navigate to the Toolbox, Spatial Analyst Tools, Surface, and choose slope.

30

This should open a dialog box where we can control the output. The Input surface should be Peavy DEM. Let’s change the Output measurement to Percent- this will give us slope values as a percent rather than degrees. Direct the output to your geodatabase and name it peavyslope. Choose the OK button.

31

Rename the new layer to Peavy Slope. Take a look at the new layer (you may have to turn the Stands layer off to see it). The legend has given us nine categories of slope.

We can use a histogram to better understand the distribution of slope values.

32

Before choosing the Histogram button however, set the Layer to Peavy Slope.

The histogram tells us that the majority of the area contains slopes in the first few categories. By clicking on a histogram bar, the slope values and number of cells for that category will be returned. Let’s close this window.

Save your map document! Raster properties From the table of contents, access the properties of the Peavy DEM layer and make the Source tab active. This should open a message box that tells you more information about the raster construction. The Data Source box tells you where this raster is stored, that it is permanent, and what coordinate system it carries.

33

When we work with the Spatial Analyst and create new RASTERs without specifying an output location and file name, temporary rasters are usually created. Temporary rasters will typically be erased when you close your ArcMap session. There is also much information in the area below the Data Source box. Most importantly is the Data type field that tells us that this is a Floating Point or decimal place raster. This means that there is no attribute table available for us to edit. If this were an integer raster, such as you would find with a nominal or character variable, we would have access to an attribute table. Cell size lists the number of units, feet in this case, per cell, and rows and columns sizes relate information about the size of this raster. Go ahead and choose OK. Save your map document before moving on Calculating average stream gradient As we just practiced, a unique feature of the Spatial Analyst is its ability to work with vector layers and rasters in the same analysis. Let’s test this feature again by calculating the average slope for streams in the Peavy area. Make sure that Peavy Slope is still the active layer in the Spatial Analyst toolbar. Choose Zonal Statistics as a Table from the Toolbox, Spatial Analyst Tools, Zonal. The Zone dataset should be streams, the Zone field should be NAME, and the Value raster should be Peavy Slope. Send the output to your workspace folder and name it “streamstat.”

34

Open the attribute table of the zonal statistics. It should look like this:

The results show that only two named streams exist in our current study area. Close this attribute table. Let’s calculate slope values for all of the roads in our study area so that we wind up with a single set of statistics for all roads. First we need to create a common field in the Roads database to summarize on. Open the attribute table for the Roads layer and choose Add Field from the Options button. If you are unable to add a field, you may have to close the ArcCatalog.

35

Enter “summary” as the name, and accept the default type of Short Integer.

Next, find the new field at the end of the Roads attribute table, right click on its title, and choose Calculate Values. Respond with a yes click when warned about editing and calculate all values for summary equal to 1.

36

Close the attribute table, and choose Zonal Statistics as a Table again from the Toolbox, Spatial Analyst Tools, Zonal menu. The Zone dataset should be Roads, the Zone field should be summary, the Value raster should be Peavy Slope, and direct the output to your working folder with the name “roadstat”.

37

A summary table should appear. This table informs us that the average slope is over 17 percent and that the maximum is over 66 percent.

Close this table and save your map document.

38

GIS LAB 7 Application: Calculating Elevation and Slope values for forested roads, streams, and stands. You will need to import the GRID that represents elevation for all of McDonald Forest. This is called “elevgrid.e00” and should be located in your workspace\gislab7\mac_lamb space. Import it, just as we did with the earlier GRID, naming it McDonald DEM and directing it to your mac_lamb folder. The elevation units are in feet. Once this GRID is imported (it’s large and may require some time so be patient), convert it to a raster within your McDonald Geodatabase. Create a new data frame called McDonald Forest and add the following layers from your McDonald Geodatabase: McDonald DEM, Roads, Streams, Stands, and Boundary. All questions that follow refer only to areas within the borders of McDonald Forest. Assignment 7. This is a team assignment. Please answer the following questions. Type your answers and turn in at the beginning of the next lab meeting. Be sure to include your names, lab day and time (e.g. Tuesday 10 AM), assignment number, and course title with your answers. Create a table for questions with more than one response. Report measurements to the nearest whole unit only. Assignment 7A. 12 points. 1. What is the average and standard deviation of elevation for areas within McDonald Forest? 2. Use the variable “standid” in the “Stands” layer to answer the following question. Which stand has the third lowest elevation and which stand has the third highest? 3. What is the average slope in percent for Baker Creek (use the name field in the streams layer) in McDonald Forest? You’ll need to derive a slope layer of McDonald Forest to answer this question. 4. What is the average slope, in percent, of rock roads in McDonald Forest? Use the field “type” within the roads layer to determine where the rocked roads are. 5. What is the average, minimum, and maximum elevation of stand 060710 (from the Standid variable)? It may be helpful for you to create a shapefile that contains only the polygon(s) from this stand before running any statistical summaries.

39

6. What is the average, minimum, and maximum elevation of roads in stand 060710 (from the Standid variable)? It may be helpful for you to create a shapefile that contains only the roads from this stand before running any statistical summaries. Assignment 7B. Create a map of McDonald Forest that shows the DEM in a five-category quantile distribution and 400 ft vertical contour lines. Include a legend for each layer in your map. Your map should contain an inset map that shows the McDonald Forest boundary within an outline of the state of Oregon (you can use the Oregon layer from Lab 6). All values on the map (DEM elevation categories and contour intervals) should not include decimals. Your map should also have a scale bar, north arrow, overall title, authors, date, and neat line. 5 points.