Exercise 5: Import Tabular GPS Data and Digitizing

Transcription

1 Exercise 5: Import Tabular GPS Data and Digitizing You can create NEW GIS data layers by digitizing on screen with an aerial photograph or other image as a back-drop. You can also digitize using imported GPS points. In this exercise we will create a simple map of pastures on the OX Ranch near the Seven Devils Mountains in Idaho. Step 1: Open a new ArcMap project. Add the four digital orthophotos from 1992 located in c:\nr402\ox\doq. The photos where downloaded from the Idaho Department of Lands web site. In this exercise you will add tabular GPS data to ArcMap and then digitize the Whitlow pasture fences into a polygon shapefile. You will then calculate the area for each pasture and add the pasture names as table attributes. Step 2: Use the below instructions to add the GPS points from the file c:\nr402\ox\gps_fence.dbf. The file is already in.dbf format so there is no need to use Excel here. The points were collected along the fence lines with a Trimble Geoexplorer 3 unit and then exported to a dbf file using Pathfinder Office. Add and display tabular GPS data to ArcGIS Tabular GPS coordinates can easily be added and displayed as points in ArcGIS. Notice that the GPS data must be in the same coordinate system as your base maps and data frame for correct display. 1. Make a spreadsheet with your X and Y coordinates in two columns in EXCEL (or other program). You can include additional columns of data in the spreadsheet as well. 2. Save your table as a dbase file (.dbf) (in this exercise your data is already in.dbf format) 3. Add the.dbf file to your ArcMap project. 4. Right-click on the table and select Display XY Data Whitlow pastures on the OX Ranch 5. Your X and Y locations will be displayed on the ArcMap screen! 36

2 Digitize fences based on GPS locations In this exercise you will digitize lines through the GPS points representing the fences and create a polygon shapefile. While digitizing, realize that the point layer is not connected to the polygon layer you are creating the points are simply there as guidance. These exercises are very simple, but will demonstrate the utility of digitizing. For a more rigorous understanding of digitizing please refer to the ArcMap help and software documentation. Step 3: Create a new (empty) polygon shapefile in ArcCatalog - Open ArcCatalog - Navigate to the folder where you want to place your new shapefile - Select File New Shapefile - Name your new shapefile and select Point, Polyline or Polygon depending on the desired feature type. In this case you want to select POLYGON. Name your shapefile fence_poly.shp. - You may also specify a coordinate system by clicking on the Edit button and the select or import an appropriate map projection. Our base maps for this project is in UTM coordinates, zone 11, datum NAD27 and mapunits meters. Step 4: Add the new and empty shapefile fence_poly to your ArcMap project. Add the Editor toolbar to your project View Toolbars - Editor (the Editor toolbar may already be in your project) Select Start Editing in the Editor toolbar make sure you are editing in the folder where your fence_poly shapefile is located. Step 5: Select Create New Feature for the Task and fence_poly for the Target. Click on the PEN and begin digitizing the first polygon click with the left mouse button with the GPS points as a guide. You don t have to click on every GPS point. After digitizing around the entire polygon doubleclick at the starting point to close the polygon. 37

3 Step 6: The next polygon you digitize will be adjacent to the first polygon they will have a shared boundary. Select Auto-complete polygon in the Task menu. Start point New polygon End point Double-click to end Begin digitizing inside the first polygon digitize around the polygon end inside the first polygon. Do not digitize along the shared boundary. Keep digitizing the three whitlow fields according to the map on page 35. If you are unhappy with the shape of a polygon select the select arrow then doubleclick on the polygon you want to modify you can now move each vertex independently. Vertex 38

4 Step 7: When you are done digitizing, select Stop Editing in the Editor menu and save your edits. The attribute table for fence_poly.shp has no attributes yet. Step 8: Use Xtools to update Area and Perimeter for the new polygons. Select Calculate Area.. in the Xtools menu. Choose fence_poly as the layer. Click OK. Step 9: In this step you will add another field to the attribute table called Pasture. You will then populate the field with the names of the pastures. Open the attribute table for the new polygon shapefile. Click on Options in the lower right corner. Then select Add Field. Name the new field Pasture. Select Text for the Type. The length defines how many letters you can have in the text description of your pastures. 50 is OK. Click OK. Step 10: You will now populate the pasture columns with the pasture names. - Select the first line in the table look at the map to see what polygon is selected - Right click on the column heading Pasture in the table and select Calculate Values in the drop down menu. 39

5 Calculate the value for the selected pasture polygons according to the map on page 36. Whitlow Field South is a text-string and must be expressed within quotation marks. OK. Select and label the remaining polygons. When you have named all pastures close the table and label the pastures on the map using the Label tab in the Layer Properties (you did this in Exercise 1). The polygons can be displayed transparent using the Display tab in the Layer Properties. 40

6 One more fence. Now you will import tabular GPS data in a geographic (degrees minutes, seconds) NAD83 map projection to ArcGIS and display with UTM, NAD27 data. 1. The GPS coordinates for yet another fence exists in c:\nr402\ox\ BroncNorthField_GEOG_NAD83.xls. The data is in Geographic coordinates (degrees, minutes, seconds) in the NAD83 datum. 2. Open the file in Excel. 3. The map projection of the aerial photos in the ArcMap project for Exercise 5 is in UTM coordinates, zone 11, datum NAD Add the Bronc Field data to the ArcMap project. The new data is another pasture that should display adjacent to the Whitlow field pastures. Digitize the additional Bronc North Field. 5. Create a map layout displaying all the pastures, scalebar etc. Hints: Convert geographic coordinates (in degrees, minutes, seconds) to decimal degrees in Excel. There are 60 minutes in a degree and 60 seconds in a minute. Remember that the longitude coordinates should be negative in the western hemisphere. Save the dataset as a.dbf file in EXCEL (this format can be easily read by ArcMap). Before you save the data as a.dbf file you may have to format all cells as numbers with 7 decimals (Highlight the spreadsheet select Cells in the Format menu format the cells as numbers with 7 decimals). If the cells are not formatted decimal numbers may not be saved in the.dbf file. It is important to save up to 7 decimals when working with data in decimal degrees. You can add the.dbf table to ArcMap and display x-y coordinates. Remember to define the coordinate system (Geographic, NAD83). 6. Create a coordinate grid over your map. Open the Layer Properties select Grids click the New Grid button. 41

7 Select Measured grid Name the grid Select Grid and labels (or as desired). Define the grid X and Y distance. 500 m works well for this example. Use the default settings through the next few screens and click Finish. The final result is a measured grid of map coordinates (UTM) overlayed over your map (in layout view). This grid can serve as important guidelines in for example a field map. This is your final map for Exercise 5. Don t forget to include a scalebar, north arrow and pasture labels (or a legend). 42