Instructors: Judd Curran & Mark Goodman Name: LAB EXERCISE #3 Data Analysis - Buffering (25pts) Transformations in GIS are methods that transform GIS objects and databases into more useful products using simple rules. These operations for the basis for many applications, because they are capable of revealing aspects that are not immediately visible or obvious. By applying transformations to your data, you can create new information that may be useful in solving a problem or answering a question. One of the more common transformations available in GIS is the Buffer operation. In this lab exercise, the buffer operation will be used to create new information that will answer a question. The Scenario: Ingrid has started a business selling used textbooks and she wants to target students for her next advertising mailer. She knows that a large percentage of GC students live within 10 miles of the campus. So, since Ingrid doesn t have a lot of cash flow, she only wants to send out fliers to those zip codes within 10 miles of the campus. The Question: What zip codes are within a 10 mile radius of the GC campus? Data Required: Campus location data (from your Lab3Data folder downloaded from the class website) Note: This folder includes GCroad.gpx GCfeatures.gpx GCcampus.jpg and requires that the gpx files be converted to.txt format by following steps contained within the GPS to GIS tutorial. Moreover the GCcampus.jpg file needs to be georeferenced (following instructions given previously) and saved as a.tiff. Zip codes data (from Sandag, under the Miscellaneous category) County Boundary data (for reference, also from Sandag, under the Jurisdiction category) LAB INSTRUCTIONS: Create a polygon layer of : 1. Create a folder on your USB drive titled campus. 2. Next, you will create a new polygon Shapefile named Grossmont. To do this, open ArcCatalog. In the Catalog Tree, navigate to your newly created folder and highlight it (by doing so, you are defining the workspace.) This will be the new directory for the new 1
shapefile. Now, select <File>, <New>, <Shapefile>. Name the new shapefile Grossmont. Change the feature type to Polygon. Click on <Edit> to select the same coordinate systems that was used when collecting GPS data for the.gpx files (Geographic Coordinate System, NAD83). Your new shapefile (Grossmont.shp) will be created and stored in your campus folder. 3. Open ArcMap with a new empty map. Add the grossmont.shp file to the map. Note that this layer will be blank, since there isn t any attribute data or features associated with it. We can create a polygon feature of the campus using the GCroad data as a reference along with the tools within the Editor Toolbar. First, let s add the GPS coordinates (see next paragraph). NOTE: Before you proceed any further, all of the lab #3 data MUST be located in the Campus folder (This includes your unzipped data from the class website and the data you downloaded from SanDAG). Use ArcCatalog to move the lab #3 data files to the Campus folder. Without consolidating your data into one folder, you will not be able to edit data or use some of the tools to work with the data. Editing will not be activated when layers within the map are stored in different folders (aka: workspaces ). If your GCroad and GCFeature tables are still in.gpx format, convert these files to.txt format and save in your Campus folder (follow instructions from your GPS to GIS tutorial handout if you don t remember how to do this). In ArcMap, select File, then Add Data, then Add XY Data... In the Add XY Data window, select the GCroad.txt file located within the Campus folder you downloaded from the class website. Then, follow instructions within the GPS to GIS tutorial to import the coordinates within ArcMap. 4. Now, let s convert the GCroad.txt XY data to a shapefile. In the Table of Contents window, right-click once on GCroad.txt Events to bring up the context menu and then choose Data, then Export Data. Export all features using the layer s source data. Then, under Output Feature Class, navigate to the Campus folder and name the output GCperimeter. 2
Choose Shapefile as the Save as File Type, then save. Add the new shapefile (GCperimeter) to the map and remove the XY data (GCroad.txt Events). Note: To save time, add the GCfeatures.txt file to ArcMAP and repeat the steps above (in step #4) to also convert the GCfeatures.txt XY data to a shapefile. 5. We can now use the GCperimeter shapefile and the Editor Toolbar to create a polygon of the campus that can be saved to our Grossmont.shp polygon shapefile. First, move the Grossmont shapefile in the table of contents to be directly below the GCperimeter shapefile. Click once on the Grossmont shapefile in the Table of Contents to highlight it. Then, click on the Editor Toolbar button to open the toolbar. Click on the Editor dropdown box in the Toolbar and select Start Editing. The Create Features window will open. Select the Grossmont from the Create Features list to initiate editing of the grossmont.shp polygon file. At the bottom of the Create Features window, choose the Polygon construction tool. 6. An editor toolbar should appear within the data window, or within the ArcMap bar at the top. In the Editor Toolbar, select the Straight Segment tool (if it is not already selected). 7. If you move your cursor over the map interface with the Straight Segment Tool active, a crosshair will appear. You will now connect the dots using the points within the GCperimeter layer to create a polygon that represents. Click once on one of the points within the GCperimeter shapefile. Then, move to the next adjacent point and click once on it to create a segment between the two points. Continue drawing line segments from one point to the next until you return to the point you started with. See notes and warnings before you start... 3
Note#1: If, in the process of connecting the dots, you have to temporarily stop to use the Pan tool or the Zoom tool, then go back to the Create Features window and re-select the Polygon construction tool. Note #2: If you accidentally make an error and add a vertex off of one of the points, right-click in the map space and select Delete Vertex. Warning: When you return to the first point to close the polygon, double-click (this is the origin/endpoint). 8. When you are finished, select the Editor dropdown button and click on Stop Editing. You will be prompted to save the edits. Click YES to save the edits. You have now created a polygon of the perimeter of saved within the grossmont.shp shapefile. You are done using the GCperimeter points as a reference to draw the campus polygon. Thus, you can remove it from the map window. In the table of contents, right-click on GCperimeter and click Remove. The point shapefile will be removed, but the new polygon of the campus will remain. Change the symbology of the Grossmont shapefile to remove the fill (hollow) and make the polygon border bold (outline width of 2) and red. Label the polygon. Note: You don t currently have this label stored within the shapefile, and thus you cannot label it until you edit the attribute table to add-in the label (see instructions below). Open the attribute table for the Grossmont layer. In the top-left corner, select the Table Options icon and choose Add Field. For the Field Name, type Name. For the Field Type, choose Text. Then, click OK. To type within the Name field that has been added to the attribute table, you must first Start Editing using the Editor Toolbar. Click on this tool and Start Editing. When the Create Features window opens, choose the Grossmont shapefile from the list. Don t bother to choose a construction tool as you 4
will not be drawing another feature. Instead, go back to the attribute table for the Grossmont layer and double click in the cell under the Name field to be able to enter text into it. Type. Back on the editor toolbar, choose Editor, then Stop Editing, then Save Edits. Close the toolbars and now label the Grossmont polygon using the Name field. Change the label text color to match the polygon outline color (red). Using the Buffer Tool: In this next exercise, we will import San Diego County Zip Codes Data from Sandag and display it with our grossmont.shp data. Then, we will try to determine what zip codes are within a 10- mile radius of the campus to identify the best locations to mail out the advertisements. 9. If you have not already done so, download the Zip Codes shapefile from SanDAG Save the Zip Codes shapefile to the Lab3Data folder Unzip it within Windows Explorer. Using ArcCatalog, move all of the contents within the Zip_Codes folder to the Campus folder. Add the Zip Codes shapefile (Zip_Codes.shp) to ArcMAP. To visualize the extent of the zip codes data, right-click on the Zip_Codes layer and click on Zoom to Layer. 10. Move the Grossmont layer to the top of the Table of Contents list so that it will display on top of the zip codes layer. 5
11. In ArcToolbox, select Analysis Tools, Proximity, then Buffer. The Buffer window will open. Perform the following to execute the buffer tool. The buffer tool will create a new polygon shapefile containing a new polygon that represents the zone around Grossmont College within 10 miles. In the Buffer window, select Grossmont as the Input Feature. For the Output Feature Class (i.e., the name and save location of the new file that will be created by this process), change it to your Campus folder, and name it GCbuffer10 (click save). For Distance, select Linear Unit. Enter 10 in the box below Linear Unit. Change units to miles using the drop-down menu. Then click OK. After a brief pause, a status bar will appear at the bottom of the map window, then the results will be displayed in the table of contents. 12. The results are a buffer polygon layer of 10 miles from the center of campus. Change the symbology of the GCbuffer10 shapefile to hollow with a bold perimeter (outline width of 2) using a color that stands out (but not red). Zoom to the GCbuffer10 layer to see the 10 mile buffer around the campus. 13. Now, let s select those zip codes that are, at least partially, within the 10-mile radius of the campus. At the top of ArcMap, click on Selection, then Select by Location. Under the Selection Method: drop-down menu, choose add to the currently selected features in. Under Target Layers, check the box next to Zip_Codes. Under the Source Layer drop-down menu, select GCbuffer10. Under the Spatial Selection Method: drop-down menu, select Target layer features intersect the Source layer feature. Then, click OK. 6
Right-click on the zip codes layer and choose Zoom to Layer to view the extent of the selected zip codes within the County that fall (at least partially) within a 10-mile radius of the county. 14. To see a list of the zip codes selected, open the Zip_Codes attribute table. Then, at the bottom of the Attributes window, click on the Show Selected Records button. All of the zip codes that fall at least partially within a 10-mile radius of the campus are displayed and highlighted. Write down how many different zip codes are found within a ten mile radius of the campus. (Note: This is also the answer to Question 21-a) 15. Now, you can separate those polygons representing the zip code areas within 10 miles of the campus from those other zip codes outside of the 10-mile radius by exporting the selected zip code polygon features to a new shapefile. To do this From the Zip Codes layer context menu, select Data, then Export Data. From the Export: drop-down menu, choose Selected Features. Use the same coordinate system as the zip codes layer (i.e., use the same coordinate system as this layer s source data ). For the Output Feature Class, choose the Campus Folder and title the new shapefile GCzipTen.shp. Click Yes to add the data to the map. Remove the full Zip_Codes shapefile from the map. Label the GCzipTen layer using the Zip field. 16. Organize your table of contents in the following order: GCBuffer10 (Top) Grossmont GCZipTen County Boundary (Bottom) 17. Zoom to a scale of 1:250,000 (you can type the scale value in the scale box in the main menu at the top of the ArcMap interface). Using the pan tool, center the map on Grossmont College. 7
18. Save the map as a PDF (File, Export Map, save as type = PDF) and name it <GcZip10lastname.pdf> Adding additional data to the campus and performing additional analysis: Now that you have some familiarity with creating new shapefiles, importing xy coordinates, converting those coordinates to shapefiles, creating features, and generating buffers, you can add additional data to the campus layer with ease! 19. In the grossmont.shp shapefile, create an additional polygon for the new science lab building (aka: Building 30 ; the building that the GIS lab is located within), using the GCfeatures data and the GCcampus.jpg (note: you will have to geo-reference this image and save it as a.tiff before it can be used) for reference and the same methods as used above: Imagine that a chemical reaction within one of the chemistry labs in building 30 has resulted in a mandatory evacuation of the building and all area within 100 feet of the perimeter of the building. o Buffer building 30 at a distance of 100 feet to identify the EVACUATION ZONE. o Create an additional field in the attribute titled NAME and in the cell for the buffered zone around building 30, type, Evacuation Zone. Then, use the NAME field to label the evacuation zone polygon. o Are there any other buildings that fall within the evacuation zone that would be required to evacuate? If so, which ones? (to identify the building/s that may be affected, reference the campus map at http://www.grossmont.edu/campus_info/map_directions.asp) o Using the same symbology and display conventions as done previously in this lab (for the other PDF), save this map on your USB drive as a PDF and name it <GcEvaclastname.pdf>. Note: Your map should include the GCcampus.tiff that you created, the new polygon shapefile of building 30, and the new buffered shapefile of building 30 8
that highlights the evacuation zone. Each of your shapefiles should be labeled and symbolized to effectively convey your results. Sending results to your instructor: 20. Attach both your GcZip10 PDF and your GcEvac PDF to an email titled <LX3lastname>. 21. Within the email that contains your attachments, send your instructor the following: a. The answer to question 14. (how many zip codes within a 10 mile radius) b. The answer to question 19. (which other buildings, if any, are within evacuation zone) NOTES: 9