Published on March 6, 2014
Exercise 3 Siting a fire tower in Loess Hills, Nebraska In this exercise, you will download and use raster and vector spatial data to decide where to site a wildfire observation tower in the Loess Hills near Blair, Nebraska. The Loess Hills represent the largest expanse of windblown silt following continental glaciation in North America. Much of the terrain, as shown in the photograph, is covered with medium-length prairie grass. The Loess Hills of Eastern Nebraska and Western Iowa USA, looking south from the Dana College Campus, Blair, Nebraska. Exercises for The GIS Guide to Public Domain Data
Context Problem Wildfires are an increasing problem, having consumed over seven million acres in the United States in 2002 alone. Wildfires in the western United States attract international attention on an annual basis, but particularly in 1988 in Yellowstone National Park, in 2005 in San Diego County, in 2007 near Los Angeles, and in 2011 in Arizona. The study area for this exercise will be the 7.5-minute x 7.5-minute cell that corresponds to the 1:24,000-scale USGS topographic map in which the town of Blair is located. Wildfires in Australia during 2011 illustrated, once again, that this hazard is a global phenomenon. To address the problem, you will download digital line graph (DLG), digital elevation model (DEM), and National Land Cover Data (NLCD) public domain data from the Internet, format the data for use in ArcGIS, and create derivative data from the DEM (a hillshade and a slope map). Finally, you will further analyze these datasets to choose the best location for your fire towers. These towers will be used by firefighters to spot wildfires and as a location for base operations for fighting wildfires in the Loess Hills near Blair, Nebraska.
Problem (contd.) The criteria for the fire towers are that they must be: Within 100 meters of a roadway, for easy access Within 200 meters of a river, for access to water At least 380 meters in elevation, for the best visibility of the surrounding terrain On a slope of less than five degrees, to minimize construction costs and maximize ground stability On pasture/hay fields, since these are the grassy areas most susceptible to wildfires in this area
Skills Required Resources Downloading and formatting public domain vector data (roads and rivers DLG) and raster data (DEM, NLCD) TIME This exercise contains seventy-two questions and will require four to five hours to complete. Managing files and data SOFTWARE ArcGIS 10.0 or later, from Esri. Merging and clipping spatial data layers Symbolizing map layers based on attribute values Analyzing raster and vector data together in a GIS environment for decision-making
Work package 1: Downloading and converting data Steps 1 - 8 In the first section of the exercise, you will download a USGS DLG from the Internet, format it for use in ArcGIS, and analyze roads and hydrography for criteria 1 and 2. 1) Preparation 2) Access the GIS data depot First, create a folder named blair (or another name that you consider appropriate, without spaces in the folder name). Go to http://www.gisdatadepot.com. This is a site run by the GeoCommunity (GeoComm), www.geocomm.com, and offers Spatial News, other information about the geospatial community, and was also one of the first sites to serve up a large amount of public domain government and other data. Some of the public domain data are free, and some are for sale; data available for sale are provided via a faster download connection. At the GIS Data Depot, select Download GIS Data and select Nebraska from the USA map that appears. 3) Find county Click Countywide Data and navigate to the county where Blair is located. GISDataDepot.com
Work package 1: Downloading and converting data 3) Find county (contd.) Steps 1 - 8 If you are not sure which county Blair is in, access another public domain data portal to find out: Open a new web browser window and access the Board of Geographic Names/USGS Geographic Names Information System (GNIS). The GNIS is a database of every name (river, peak, town, cemetery, etc) that occurs on USGS topographic maps. The GNIS is on: http://geonames.usgs.gov. Using Geographic Names Information System. 3.1) What county is Blair in?
Work package 1: Downloading and converting data 4) Accessing the DLG data Steps 1 - 8 Go back to the GIS Data Depot window. Click the correct county, and then select Digital Line Graphs (DLG) 1:24,000-scale. On the following screen, you will see a green download button and a brown download button to the right of each DLG in the county. The green button (normal downloads) is the one you should use. Each DLG corresponds to a 7.5-minute x 7.5-minute block of the earth’s surface (one topographic map at 1:24,000-scale). Note: You will need to create a GeoComm account to download the data. You won’t receive promotional e-mails as long as you’re careful not to select any boxes that state “Please send me information about . . .”. 5) Download Roads and Hydro data After creating your account, download the Roads and the Hydro file for the Blair 7.5-minute x 7.5-minute cell. The vectors you are downloading are in SDTS format. Read a bit about SDTS format on http://data.geocomm.com/sdts/ 5.1) What does SDTS stand for, and what is the purpose of this format? SDTS is very particular about the location of the data in relation to the master data dictionary, which contains information that the SDTS files need to access. Make sure you select the green (normal downloads) buttons and not the (premium downloads) buttons. Save the files but do not unzip them.
Work package 1: Downloading and converting data 5) Download Roads and Hydro data (contd.) Steps 1 - 8 Make sure that you download five zipped files in gz format, as follows: • One masterdd (master data dictionary) zipped file into a folder named masterdd. This folder must reside one level up from the folder(s) where your data resides. • One hydrography zipped file. • Three transportation zipped files. Download Digital Line Graph files for Blair, Nebraska.
Work package 1: Downloading and converting data 5) Download Roads and Hydro data (contd.) Steps 1 - 8 Note: The DLG data from GIS Data Depot is also available directly from the organization that produced it, on the following USGS FTP site: http://edc.usgs.gov/geodata Navigate via state or alphabetical list until you are on the 1:24,000-scale DLGs: http://edcftp.cr.usgs.gov/pub/data/DLG/LARGE_SCALE/B/blair_NE If you wish to use this site, you won’t need a user account. 5.2) Why do you think that the GeoCommunity, through the GIS Data Depot, can supply the same data that the US government provides? Name at least two things about the GIS Data Depot’s service on GeoCommunity that represents value added over the government’s portal for the same data. Go to page 12 of the USGS standards for DLGs, at: http://nationalmap.gov/standards/pdf/1dlg0798.pdf 5.3) Name the type of transportation that is associated with the following files that you downloaded: Code RD RR MT Type of Transportation
Work package 1: Downloading and converting data 6) Download setupdlg.exe Steps 1 - 8 ArcGIS cannot directly import SDTS formatted DLG files. It can import SDTS point data—but not the line data that you need to solve your fire tower problem. Find the DLG2SHP program at the Tennessee Electronic Atlas: http://tnatlas.geog.utk.edu/tea/ You will find it under Download: Software for working with Census TIGER files, Summary Files, and USGS Digital Line Graphs. Find the file DLG2SHP and select Setup Program. Save the file Setupdlg.exe. You may need to adjust some settings on your computer’s security system so that you can run executable (.exe) files. Sometimes these files are blocked because viruses can be distributed through exe files. The setupdlg executable is not a virus, but rather installs a program that will convert your SDTS DLG to a shapefile. Read the background information about how to run this program from the User Manual that was available for download along with the Setup Program: http://tnatlas.geog.utk.edu/freeware/dlgmanual3.pdf Run the setupdlg.exe program on your computer. This will run an install program and create a program group for you. After installing the program, you should now have a choice on your Programs menu called GIS Tools. Under GIS Tools is the DLG2SHP program.
Work package 1: Downloading and converting data 7) Convert SDTS data Steps 1 - 8 Run DLG2SHP. The program should look similar to the interface shown next. Add your two .gz files—the hydro and only the roads layer located under transportation (since that is the only layer that you need to make your fire tower decision), and note your output folder names. Converting DLG files to shapefiles. Note: The DLG2SHP program can process the unzipped .gz files directly. If you were not using this tool, you may have to unzip the files. Before you extract the files, uncheck the WinZIP setting for TAR file smart CR/LF conversion. The location of this setting may be slightly different depending on your version of WinZIP, but is usually under Options > Configuration. Sometimes, the CR/LF (Carriage Return/Line Feeds ) setting causes problems with GIS software being able to read your SDTS spatial data.
Work package 1: Downloading and converting data 7) Convert SDTS Data (contd.) Steps 1 - 8 The reason is that the SDTS data comes in a long string, and the CR/LFs break up the data strings and make it unreadable. Click Yes, if WinZIP asks you if you wish to decompress to a temporary folder and open. Edit the Output Directory to make sure you know where the converted datasets will be stored and edit the directory path if needed. Select GO in the DLG2SHP program. Navigate to your output directory. You should see two new folders, one for the hydrography and one for the roads. 8) Access the downloaded data Start ArcGIS and access the Catalog within ArcMap by using Windows > Catalog. Establish a connection to the folder where your Blair data are located, and navigate to this folder. 8.1) Preview the geography for the five different shapefiles (shp) for hydrography and for roads. Briefly describe the appearance of the following: Hydrography LE01 NA01 N001 NP01 PC01 Roads
Work package 1: Downloading and converting data 8) Access the downloaded data (contd.) Steps 1 - 8 8.2) Which hydrography shapefile do you think you will be using for this exercise, if you need hydrography as line data? 8.3) Which roads shapefile do you think you will be using for this exercise, if you need hydrography as line data? 8.4) Right-click your layer name in ArcCatalog and access the description. Look under the spatial description and check the coordinate system of your data. Does the description provide any sort of projection and coordinate system? 8.5) Using Windows Explorer, navigate to your output DLG folders for hydrography and transportation. Examine the Word (DOC) files that are in each folder. Do these documents provide any sort of projection and coordinate information? If so, what projection and coordinate system do you suspect these datasets are in? Sometimes when you are working with public domain spatial data, the metadata are not complete, but the data are nevertheless cast into a specific projection and coordinate system. End of work package
Work package 2: Viewing and manipulating data 9) Add the data to ArcMap Steps 9 - 19 Start ArcMap and start a new empty map. Click the Add Data button and add the hydrography and roads files that you identified above. Add them as line data, rather than point or polygon data. You should receive a message from ArcMap indicating that it does not know the coordinate system of your data. This can be ignored for now; you will deal with projections shortly. Examine the USGS UTM fact sheet on the universal transverse Mercator coordinate system: http://erg.usgs.gov/isb/pubs/factsheets/fs07701.html 9.1) Examine the location of Blair against the map of the continental USA on this fact sheet. Which UTM zone is Blair in? Verifying hydrography and roads data.
Work package 2: Viewing and manipulating data 9) Add the data to ArcMap (contd.) 10) Recast the data Steps 9 - 19 9.2) Now consider where Blair is located in relationship to its UTM zone in the map on the USGS UTM fact sheet. In your ArcMap session, why does the 7.5-minute cell for Blair appear to be tilted, with the northeast corner appearing farther north than the northwest corner, and the southeast corner appearing farther north than the southwest corner? Under View > Data Frame Properties > Coordinate System, change the data frame to Predefined, Projected Coordinate Systems, UTM, NAD 1983. Assign the appropriate zone for Blair (from your analysis of the USGS UTM Fact Sheet). Note: This does not change the projection of the datasets, but rather, recasts them into a UTM data frame. In other words, they will look like UTM, but they are still unprojected data. 11) Save your map document 12) Check the data Save your map document, with a suitable name, to your working folder. Next, recalling the original fire tower problem, you need to buffer the roads and hydro to select the areas that are within 100 meters of roads and 200 meters of rivers to consider for your fire tower locations. However, first toggle the two layers on and off and consider the following before you buffer. 12.1) Are all of the features in the hydro layer actually rivers? Are all of the features in the roads layer truly road features? Why or why not?
Work package 2: Viewing and manipulating data 13) Select by Attribute 14) Recast the data Steps 9 - 19 Find an attribute in the table for hydro and roads that would allow you to use Select by Attribute to narrow down your dataset for only features that are actual roads and hydrography. Select the outer boundary lines in your dataset. 14.1) Are all of the features in the hydro layer actually rivers? Are all of the features in the roads layer truly road features? Why or why not? 15) Select roads and hydro features Once you have selected these roads and hydro features that are actually neat lines, use Selection > Switch selection to select those lines in the roads and hydro layers that are actually roads and hydro features. 16) Buffer the roads Use Windows > Catalog and navigate to Toolboxes > System Toolboxes. In the System Toolboxes, select Analysis Tools > Proximity > Buffer to buffer the roads according to the criteria for your fire towers. Save as a shapefile in your working folder. Delete “use”. 17) Buffer the rivers Next, buffer the rivers according to the criterion for your fire towers. Remember that this criterion is different than that for the roads. Save as a shapefile in your working folder. Zoom in on a few of your buffers and use the Measure tool to answer the following question.
Work package 2: Viewing and manipulating data 17) Buffer the roads (contd.) 18) Intersect roads and hydro data Steps 9 - 19 17.1) Are the buffers of x meters x meters on each side of the feature, or x meters total? In other words, are your 100-meter buffers 100 meters on each side of roads, or 100 meters across the width of the buffer? Next, in the Systems Toolboxes, Use Analysis > Overlay > Intersect to intersect your roads and hydro buffers. Your output (near_rds_near_hydro) will represent land that is near roads and near hydro features. 18.1) Perform a visual inspection of your map. How much of the Blair terrain would you estimate is currently under consideration for your fire towers? 19) Save Remember to save your map document often! End of work package
Work package 3: Downloading elevation and land cover data Steps 20 - 39 Now that you have selected areas near roads and streams using your DLG data, you are ready to address criteria 3, 4, and 5 for your fire towers: on high elevation, low slope, and on pasture/hay land use. To address these criteria, you will need to download and format two more types of data: • DEM data. These DEMs been vertically integrated with hydrography data, standardized on elevation units, and edge joined with adjacent DEMs to form the National Elevation Dataset (NED). • 1992 NLCD to determine where pasture/hay (and thus, grassy) areas exist. You will download both of these datasets from the USGS seamless data portal. On this portal, as the name implies, data are not stored by county or in 7.5-minute blocks. The user defines the block that he or she needs. To easily download the data block that corresponds to the 7.5-minute area of Blair, you will need to find the latitude and longitude for the Blair block. 20) Find Blair Open a new web browser window and access the USGS GNIS. As you know from when you accessed this site earlier in this exercise, GNIS is a database of every name that occurs on USGS topographic maps, at: http://geonames.usgs.gov. Query US States and Territories and find Blair, Nebraska as a Populated Place. 20.1) What is Blair’s latitude and longitude? You need to find the 7.5-minute latitude-longitude block into which Blair falls. You can obtain a paper USGS topographic index to find out the correct map name on which the town of Blair exists. However, it is far easier to check the scanned topographic indexes online.
Work package 3: Downloading elevation and land cover data 21) Access topographic map index Steps 20 - 39 Access USGS Topographical Maps at http://www.topographicalmaps.com. USGS Topographical Maps.com is a distributor of USGS maps, and one of their services is a free online topographic map index. USGS topographic map index. 22) Query the index On the map, click the state where you are siting the fire tower and zoom in. You will first see the index for the 1 x 2 degree series (1:250,000 scale). Clicking on this map reveals the 30 minute x 60 minute series (1:100,000 scale) index.
Work package 3: Downloading elevation and land cover data Steps 20 - 39 22) Query the index (contd.) USGS topographic indices. 22.1) What is the 1:250,000 scale map (1 degree x 2 degree block) name that includes Blair? 22.2) What is the 1:100,000-scale map (30 minute x 60 minute [½ degree x 1 degree) block] name that includes Blair?
Work package 3: Downloading elevation and land cover data 23) Examine map names Steps 20 - 39 Clicking on the 1:100,000-scale map on Blair index yields the map index containing all of the 7.5-minute x 7.5-minute blocks. These are the 1:24,000-scale maps. Examine the map names that make up the Blair 1:100,000-scale block. Note that one of the 7.5-minute cells is named Blair. This is the cell in which you downloaded and worked with the hydrography and roads layers earlier. USGS 1:24k (7.5 min) topographic map quads.
Work package 3: Downloading elevation and land cover data 23) Examine map names (contd.) Steps 20 - 39 23.1) For the 7.5-minute cell that covers Blair, indicate the southeast and the northwest (minimum and maximum) latitude and longitude coordinates in decimal degrees (for example, 36.500 format rather than 36 30´ format), in the boxes below: Minimum Maximum Latitude Longitude 23.2) Now, write down the southeast and the northwest (minimum and maximum) latitude and longitude coordinates in degrees, minutes, and seconds that bound the 7.5-minute area that covers Blair. Minimum Latitude Longitude Maximum
Work package 3: Downloading elevation and land cover data 24) Examine map names Steps 20 - 39 Access this site, http://seamless.usgs.gov, for your elevation and land cover data. You may have noticed that on your County page on gisdatadepot.com, some of these datasets were available from the GeoCommunity. However, the only selection available for some of this data was premium download, for which you have to pay. Companies like GeoComm resell government data. They provide a convenient, one-stop service, with tutorials and an organized structure. One has to weigh the costs and benefits of obtaining data for free, which often requires more processing stages, versus paying for already processed data, where one can save time and effort, and sometimes have more choices on the projections, media, and formats in which the data are offered. 24.1) Why do you think you will access the seamless USGS data server for the rest of the data for locating the fire tower instead of staying at GIS Data Depot?
Work package 3: Downloading elevation and land cover data 25) USGS Seamless Viewer Steps 20 - 39 On the http://seamless.usgs.gov server, access the Seamless Viewer link. After the viewer appears on the left, under Downloads, select Define Download Area by Coordinates. You will see the following screen: Defining an area of interest by coordinates on the USGS seamless data server. 26) Specify area of interest Enter the minimum and maximum extent for the 7.5-minute block that you need for your study, entering the coordinates that you wrote down earlier. Use either degrees-minutes-seconds or decimal degrees, but select the appropriate screen for each format. After entering your coordinates, select Add Area.
Work package 3: Downloading elevation and land cover data 27) Select the data Steps 20 - 39 You will see a screen titled Data Extraction Request Pieces. Use Modify Data Request and do the following: Unselect the 1 arc second NED data. This 30-meter horizontal data is not of sufficient resolution for your study. Change it to the 10-meter horizontal NED data (1⁄3 arc second) to accurately site your fire towers. Select the 1992 National Land Cover Data (resolution 30 meters) data. Indicate that you would like the data delivered in Arc Grid format. Click Save Changes & Return to Summary. Note: The USGS seamless data server is useful, but it is notorious for its security setting requirements. If you cannot download your data, you may have to temporarily allow pop-ups in your web browser on this site. If you have enabled pop-ups but still cannot download your data, go to the security settings on your web browser. You may have to add http://seamless.usgs.gov and possibly even http://extract.cr.usgs.gov to your list of trusted sites.
Work package 3: Downloading elevation and land cover data 27) Select the data (contd.) Steps 20 - 39 Your screen should look similar to the following: Confirmation of data summary from USGS seamless data server.
Work package 3: Downloading elevation and land cover data 28) Extract the data Steps 20 - 39 Click Download for both data sources to be added to the queue. When your data are ready, you will receive a prompt. Notification from USGS National Map Seamless Server that a data package is available to download. 28.1) In what spatial data format will the NLCD and NED data be in when you download it to your local computer? 29) Download the land cover data Create a folder named nlcd or landcover under your Blair folder and download the landcover data into this folder.
Work package 3: Downloading elevation and land cover data 30) Download the elevation data Steps 20 - 39 Create a folder named ned or elevation under your Blair folder and download the elevation (NED) data into this folder. 30.1) Why is the NED data block larger in file size (in megabytes) than the NLCD block? 31) Unzip the data Extract or unzip the files that you have downloaded using WinZIP or other suitable program. Be sure to keep the output name brief, and without any spaces, as these datasets will be raster (grid) data. 32) Examine the data Using Windows Explorer, navigate to the folder where the NED and NLCD datasets are stored. 32.1) How is ArcGrid raster data stored on your computer? 33) Add the data to your map document Add the elevation data and the land cover data to your Blair ArcMap document (not the metadata.shp file, but the raster data): Adding elevation and land cover raster data to ArcMap. Note that the number assigned to your elevation and land cover data may vary from the image shown.
Work package 3: Downloading elevation and land cover data 33) Add the data to your map document (contd.) Steps 20 - 39 33.1) Which of the two layers can be displayed in your map—elevation or land cover? When one layer will not overlay your other data layers, it usually means that the map projection for that layer is not set or is incorrect. 33.2) Can you determine what the map projection is for the elevation data layer by examining the metadata within the Catalog in ArcGIS? If so, what is it? 33.3) Can you do the same for the land cover data layer? If so, what is it? 34) Project the land cover data Define the projection for the land cover data so that you can work with it. Sometimes, the metadata for a layer are not present. However, by further investigation outside ArcGIS, and analyzing files that you may downloaded along with the data, you can sometimes determine the map projection and coordinate system for a data layer. In the case of the land cover data, use Windows Explorer to find the file <number>_meta1.txt, where <number> corresponds to the numbered name assigned to your land cover data when you downloaded it (for example 23235535_meta1.txt). Open this file in Notepad.
Work package 3: Downloading elevation and land cover data 34) Project the land cover data (contd.) Steps 20 - 39 34.1) Is this file a very convenient way to store and access metadata information? The file may not be easy to use, but it contains vital information for working with the data layer. In the file, use Search (control-F) to find the text string Horizontal_Coordinate_System_Definition. 34.2) What is the map projection for this dataset? 34.3) What is the first Standard Parallel, the second Standard Parallel, the Longitude of the Central Meridian, and the Latitude of the Projection Origin for this dataset? Use the Catalog to find Toolboxes > System Toolboxes, and then search for the tool Define Projection. Define the projection for the land cover data layer based on your answers above. Because this projection is frequently customized depending on the public domain spatial data provider, be certain to modify the projection based on your information about the first and second parallels, the central meridian, and the latitude of the projection origin, according to your answer above, as follows:
Work package 3: Downloading elevation and land cover data Steps 20 - 39 34) Project the land cover data (contd.) Defining the projection parameters for the land cover data. 35) View the data After projecting your land cover data, your land cover data should overlay with the other data layers in ArcMap. Your map document should look similar to the following; you should see four layers, including hydrography, roads and trails, land cover, and elevation.
Work package 3: Downloading elevation and land cover data Steps 20 - 39 35) View the data (contd.) Viewing the elevation, hydrography , and transportation data for Blair, Nebraska. 35.1) What are the lowest and the highest elevations for this area? (And you thought Cornhuskerland was flat!). 35.2) Examine the metadata for the elevation data. What are the units for the elevations–feet or meters? 35.3) Are the NED (elevation) and NLCD (land cover) datasets raster data or vector data?
Work package 3: Downloading elevation and land cover data 36) Turn on Spatial Analyst extension 37) Selecting elevation criteria Steps 20 - 39 In ArcMap, access the Spatial Analyst extension by using Customize > Extensions to turn on the Spatial Analyst Extension. You will need this extension to analyze your new raster data layers. You need to select certain elevations that meet your criteria. Examine the Selection > Select by Attributes pull-down menu. 37.1) What layers can you use Select by Attribute on? 37.2) Why can you not select elevations by attribute? The elevation data is raster, and you will therefore need another method to select the raster pixels that meet the criteria, which is equivalent to the Select by Attribute method for vector data. 38) Using the raster calculator In Catalog, navigate to Toolboxes > System Toolboxes > Spatial Analyst Tools > Map Algebra > Raster Calculator, or use the Search function to search for and find the Raster Calculator. Use the Raster Calculator to select areas that meet the elevation criteria for your fire towers. Make sure that you store your output raster layer in your working folder. 38.1) What expression did you use?
Work package 3: Downloading elevation and land cover data 39) Examine new layer Steps 20 - 39 Examine your attribute table for your new layer. 39.1) How many cells are suitable for the fire tower in terms of elevation? 39.2) What percentage of your study area is suitable in terms of elevation for your fire towers? Show your work. 39.3) Recalling the resolution of your elevation data, how much land area is suitable in square meters and in square kilometers? Show your work. You now have met criteria one, two, and three for your fire towers: Close to roads, close to hydro, and on high ground. Remember to save you map document. End of work package
Work package 4: Creating a slope layer Steps 40 - 47 Criterion four calls for a slope of less than five degrees to minimize construction costs and maximize ground stability, so you will need to create a slope layer. 40) Create slope layer Use the Spatial Analyst Tools > Surface > Slope tool to create a Slope raster layer. Make sure your slope layer is in degrees, not percent. Examine the resulting slopes. 40.1) What is the problem with the slopes values across the map? The problem exists because the data from the seamless USGS data server are not in any projection, but in geographic coordinates, latitude-longitude, mapped in the Data Frame to look like UTM. The horizontal units (degrees) do not match the vertical units (meters), and so the slopes are incorrect. Therefore, you need to project the DEM/NED data, not just setting the data frame to look like UTM. 41) Project raster data Under System Toolboxes, use Data Management tools > Projections and Transformations > Raster > Project Raster to project your raster data. Use your original DEM as your input raster, and give the name ned10mutm (for your 10m NED data in UTM) and location for your output raster. 42) Choose coordinate system For the projection, Select a Predefined Coordinate System. Choose UTM and the zone you determined earlier, as follows:
Work package 4: Creating a slope layer Steps 40 - 47 42) Choose coordinate system (contd.) Selecting a coordinate system for the elevation data. Note: Remember to save your map document often! 43) Remove layer 44) Create new layer Remove your erroneous slope map layer from the table of contents. Create a new slope map using your projected DEM data as the input layer. 44.1) Describe the slopes across your study area. 44.2) What is the correct maximum slope in the dataset?
Work package 4: Creating a slope layer 45) Identify slopes less than five degrees 46) Elevation and slope criteria Steps 40 - 47 Use the Raster Calculator to select cells that are less than five degrees slope. Name this new layer as SlopeUnder5 and save in your working folder. 45.1) How much of the land area in your study area is suitable in terms of slopes for your fire towers? Show your work. Next, use Raster Calculator to create a raster layer that meets both the elevation and slope criteria. Name your new layer elevokslopeok. You may receive a projection message since your DEM data is in UTM. 46.1) What expression did you use to accomplish this? 47) Hillshade tool Next, use the Spatial Analyst Hillshade tool to create a hillshade of the UTMprojected DEM for your study area. 47.1) What is the name of the landform represented by the flat area in the northeast corner of your study area? Use additional map sources if you need help in determining what this landform is. End of work package
Work package 5: Converting raster data to vector format Steps 48 - 59 You have addressed the first four criteria for your fire tower analysis: Close to roads, hydro, on high ground, and on flat ground. Next, you will address the last criterion—locating the fire tower on grassy areas. 48) Examine NLCD layer Make the NLCD layer visible. Examine the NLCD attribute table for Blair and the legend underneath the NLCD layer name in the table of contents (to the left of the map). 48.1) What do the numbers in the NLCD legend in ArcMap mean? 48.2) Based on the count of cells in the attribute table, what are the two most common land use types in this area? 49) Examine metadata Examine the metadata for the NLCD that you downloaded with the data. The metadata should be in a file named <number>meta1.txt in your NLCD folder, where <number> represents the file name/number from the USGS seamless data server. 49.1) Is this file easy to read? Why or why not? 50) Examine land use codes Search on the phrase Entity_and_Attribute_Overview in this metadata file. This phrase marks the beginning of the section containing the land use codes and their descriptions. 50.1) What is the land use for the two most common land use codes in the study area that you identified earlier?
Work package 5: Converting raster data to vector format 51) Using Raster Calculator Steps 48 - 59 Use the Raster Calculator to create a layer that encompasses criteria three, four and five; that is, the elevation, slope, and land use are all acceptable. 51.1) What expression did you use? 52) Change the default settings for new rasters Right-click this layer and access its source. This layer is temporary if you have not yet changed any settings; temporary is the default setting for new rasters created. You can make layers resulting from raster processing permanent by accessing Geoprocessing > Geoprocessing Options, and unchecking Results are temporary by default, as follows: Setting the geoprocessing options.
Work package 5: Converting raster data to vector format 52) Change the default settings for new rasters (contd.) 53) Make the raster layer permanent Steps 48 - 59 52.1) What is one advantage of having your raster layers as temporary files? 52.2) What is one advantage of having your raster layers as permanent files? If your layer representing suitable elevation, slope, and land use is not already permanent, make it so by right clicking the layer, Data > Export Data, making it permanent, and giving it a suitable name (brief, short, and without spaces, since it is a grid). This is a raster decision grid that represents results of criteria three, four, and five. Data used in criteria one and two are vector layers. Because of this mixture of vector and raster, you cannot overlay all of these layers yet. To consider ALL criteria at once, you must either convert your raster layer to vector and complete the analysis, or convert the vectors to raster. Each has its advantages, but it is important that your final land parcels where you consider siting your file towers will be slightly different depending on whether you choose the vector or raster route. For this exercise, let’s convert the raster layer to vector and do the rest of the analysis on vector data.
Work package 5: Converting raster data to vector format 54) Convert raster layer to vector Steps 48 - 59 Use System Toolboxes > Conversion Tools > From Raster > Raster To Polygon. Convert your raster layer representing suitable elevations, slopes, and land use to a polygon shape file, as follows: Converting raster data to a shapefile. 54.1) Why will the results be slightly different depending on whether you use vector versus raster processing methods? 55) Alter symbology Make the symbology for this new vector layer hollow so you can see the raster layer it came from underneath. Zoom to a few of the polygons. 55.1) What vector shape resulted from the few square grid cells that were on their own in the raster format?
Work package 5: Converting raster data to vector format 56) Examine polygon layer 57) Summarize field Steps 48 - 59 Examine the attribute table for your resulting polygon vector layer. 56.1) What is the name of the field that indicates whether a polygon is suitable? Open the attribute table, right-click the field that you indicated above, and perform a summarize on this field that indicates suitability. This will create a summary table, as follows: Generating a suitability summary table on your elevation, slope, and land use.
Work package 5: Converting raster data to vector format 58) Examine summary table 59) Symbolize vector layer Steps 48 - 59 Open the new summary table. 58.1) How many polygons meet the criteria in terms of elevation, slope, and land use? Symbolize this vector layer as a unique-value map based on the field name so that the suitable polygons are one color and the other areas that are not under fire tower consideration are another color. Note: Remember to save your map document often. You are now ready for the final analytical steps. End of work package
Work package 6: Interrogating the data 60) Examine summary table Steps 60 - 67 Select the polygons that meet the criteria in the polygon layer that you have been working with (the layer that includes considerations of elevation, slope, and land use). 60.1) What was your expression to accomplish this selection? 60.2) How many polygons have you selected? Fill in the blanks below: ___________ of ____________ 60.3) Do you notice a spatial pattern in the areas under consideration? If so, what is it? 61) Export to shapefile Use Data > Export Data to export the selected features to their own shapefile, called pasture_hay_elev_slope_ok_final.shp or some other suitable name. 61.1) What are the differences between the original pasture/hay/elevation/slope OK vector polygon layer and the new one you just created, and why was the creation of this new layer necessary? Now you’re ready to intersect the layer containing areas where the land use, elevation, and slope are suitable with the areas near hydro and near roads for the final sites to be considered for your fire towers.
Work package 6: Interrogating the data 62) Intersect layers Steps 60 - 67 In the Systems Toolbox, use the Analysis > Overlay > Intersect function to intersect the following: elevok_slopeok_landok - your suitable elevation-slope-land use areas layer WITH near_rds_near_hydro - your suitable close-to-roads and close-to-hydro areas layer (recall that this is your layer from step 18) Name your output layer final_sites.shp. 63) Examine final sites Examine your final sites layer. 63.1) In which regions of the study area are you now considering the placement of your fire towers? 63.2) If you only had the funds for one fire tower, how important would it be to see the town of Blair from the fire tower? 63.3) Where would you say is the largest concentration of suitable polygons in relation to the town of Blair? These areas that are clustered near Blair are the ones you will consider as the most suitable candidates for your tower location. 63.4) How far is this concentration of suitable areas from the town of Blair?
Work package 6: Interrogating the data 64) Create a layout Steps 60 - 67 Use View > Layout View to create a layout that includes: • Your final sites shown on top of a Hillshade. (A hillshade is made with the spatial analyst toolbox.) • An appropriate title, author, north arrow, and legend. • Include any other layers you think are appropriate, such as roads or hydro, with suitable symbology. 64.1) Paste this layout into this exercise document or save as a separate file. 65) Analyze final study sites Analyze your final study sites. 65.1) Speculate as to the differences in your final sites if you had made the final analysis a raster-based analysis instead of a vector one. 65.2) What steps would you have had to perform in ArcGIS to make the final analysis a raster instead of a vector?
Work package 6: Interrogating the data 66) Consider general context Steps 60 - 67 Consider the problem in a more general context. You have now considered several factors for the location of your fire observation towers and used public domain data in your decision. 66.1) What other criteria might you want to consider if you had more time and funding for locating fire towers in this region or in any other region? 66.2) What public domain or other data would you need to consider these extra criteria? 66.3) Which agencies or organizations could produce the additional data that you need for this project? 66.4) Summarize what you learned about public domain data in this exercise. 66.5) Summarize what you learned about ArcGIS in this exercise. 67) Save and exit Save your map document and close ArcMap. End of work package
Chapter 3 quiz 1) What is the difference between discrete and continuous raster data? Give an example of a public domain dataset in each of these two categories. 2) Name the four types of raster resolution. 3) Name three types of raster data and the organization that produces each type. 4) Describe two developments over the past twenty years that have enabled raster data to become more widely used. 5) What is the difference between a DEM and a hillshade? 6) Which issue surrounding spatial data privacy do you think will be of highest concern throughout the remainder of this decade, and why? 7) Which principle in handling personal data identified by Onsrud, Johnson, and Lopez do you consider to be most important, and why? 8) What was the easiest and most difficult dataset to work with regarding your analysis of the Blair fire towers, and why? 9) Did the data you used to site the fire towers have any issues regarding privacy? Why or why not? 10) What other problem could you apply the DEM, land cover, road, and hydrography data to besides siting fire towers?
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