Digitizing Tutorial
The process of creating GIS data is known as digitizing. We are going to generate some GIS data -- the Spartanburg Water Districts boundaries -- from scratch. You can create blank geographic data using ArcCatalog, and then edit the data using ArcMap. As we discussed, the data can be created as basic Shapefiles OR as file geodatabase feature classes, which provide additional speed and functionality. This tutorial will demonstrate how to create polygons in a Shapefile, but the process is very similar for creating a feature class in a geodatabase.
This tutorial continues from the end of the Georeferencing tutorial. You should now have a georeferenced raster dataset of the Spartanburg Water Districts.
Getting Started:
Open the map document you created in the Georeferencing tutorial OR create a new, blank map.
In ArcMap, maximize the ArcCatalog pane on the right side of the screen (if necessary).
Connect to the local LadnerCI folder (if necessary).
Add the SpburgWater_georef.tif raster dataset created in the previous tutorial to the map (if necessary).
Add the Counties_SC.shp shapefile to the map (if necessary).
Change the Counties_SC layer symbology to hollow with a brightly colored outline.
Creating an Empty Shapefile
We need to make the shapefile for the water district polygons. When we create the feature, we can assign our chosen coordinate system (South Carolina State Plane).
Right click on the LadnerCI folder in the ArcCatalog pane.
Move your mouse over and select New and click Shapefile. A dialog box will appear.
Name the new file "WaterDistricts" (without spaces!). Set the Feature Type as Polygon.
Click the Edit button. Set the XY Coordinate System to Projected Coordinate Systems>State Plane>NAD 1983 (2011) (Meters)>NAD 1983 StatePlane South Carolina III FIPS 3900.
Click OK. The WaterDistricts layer shows up at the top of the Table of Contents.
Editing Your Data
Now that you have created an empty shapefile, we can begin to populate them with data. This is accomplished using the Editor toolbar in ArcMap. We will start an editing session in which new features can be drawn, edited, and/or deleted. (Note that we are going to create polygons, but the process for creating lines and points is very similar).
1. Zoom in to the SpburgWater_georef raster so that the gray water districts in Union, Cherokee, and Landrum counties are framed in the map area.
2. Click on Customize > Toolbars > Editor to turn on the Editor toolbar.
3. In the editor toolbar, click Editor. In the dropdown menu, click Start Editing.
4. Click the Create Features button on the right handside of the Editor toolbar. A new frame will appear on the right side of the screen.
5. At the top of this frame you will see polygon symbol (a box) and the name WaterDistricts. Click on it.
At the bottom of this frame, the Construction Tools options will appear. The default is to build a polygon using the Straight Segment tool. This will create a polygon with vertices (corners) everywhere you click on the screen. This will work well for tracing the edge of the Water Districts boundary. Notice that the cursor turns into a + when it is moved into the map area.
We are going to start drawing in the water district boundary in the southeast corner of the district, south of the words "Union Co." and northeast of the words "Wholesale Water Service."
6. Zoom in to the southeast corner of the water district using the mouse wheel.
7. Begin the polygon by clicking on where the eastern district boundary meets the southern district boundary/county line.
Notice that if you move the mouse around, a line between the point you clicked and the cursor is created.
TIPS: Zoom in/out with the mouse wheel and pan the view by holding the mouse wheel and dragging the map as needed. You can hit ESC to quit your drawing and begin again if you make a mistake.
Notice that small, shaded areas will fill in next to the points you click. These may show up on the wrong side of the boundary line until we have drawn the polygon completely.
8. Click to add points along the eastern boundary in a northern direction. Use as many points as necessary to get an accurate boundary line.
8. Add points until you get near the Cherokee County Line. Click a point directly on the county line in the Counties_SC layer.
We have this excellent county boundary line in the Counties_SC layer which seems to coincide with the water district boundary in some areas. Let's trace this boundary to create the edge of the water district.
9. In the Editor toolbar, click the Trace tool.
10. Click on the last point you created on the county line -- it should be red, not green. This will start the Trace tool.
11. Slowly move your mouse along the county line. Notice that a line is being traced over the county line -- it's gray on my screen.
12. Continue tracing the county line to the east, using the mouse button to zoom and pan around as needed.
14. Click the Trace tool again and click on the last point you created (the red vertex). Trace the county line northward until the water district bound separates from the county line.
13. Trace until you reach the eastern edge of the water district and county. Click once where the county lines intersect.
15. Click on the Straight Segment tool on the Editor toolbar. Click points along the northern edge of the water district to draw the boundary as before.
16. Use the Trace tool to follow the county lines where possible, and use the Straight Segment tool to finish the other edges.
17. Double click the mouse to finish the polygon.
File Geodatabase Feature Classes
Creating an Empty Feature Class
Creating an empty feature class that resides in a file geodatabase could be used for the water district boundary polygons instead of a shapefile. To create the file geodatabase and feature class is a straightforward task.
1. Right click on the LadnerCI folder in the ArcCatalog pane.
2. Move your mouse over and select New and click File Geodatabase. A new icon is added in the folder. Rename it Spartanburg.gdb.
3. Right click on this geodatabase and move your mouse over New and click Feature Class
4. In the new dialog box, enter "WaterDistFC" in the Name field.
5. Set the type of features stored in the feature class to Polygon Features (if not automatically selected). Click Next.
6. In the next screen, choose the same coordinate system as above: NAD 1983 (2011) State Plane South Carolina FIPS 3900.
7. Click Next and continue accepting defaults and clicking Next until you are able to click Finish.
Editing Your Data
Creating the polygons during an editing session occurs exactly the same as for a shapefile. You begin an editing session, use the editing tools to create features, save your edits, and quit the session.
Converting Between Feature Classes and Shapefiles
It is possible to export feature classes from a geodatabase as shapefiles if you need to share a single feature class. You can also import shapefiles into geodatabases to take advantage of their features, such as automatic area calculations. Let's import our WaterDistricts.shp shapefile into the Spartanburg geodatabase as an example.
We have our first polygon feature. Let's save the changes. If you leave an editing session without saving the edits, any changes will be lost!
18. On the Editor toolbar, click the Editor dropdown and select Save Edits.
You can repeat this process to create all the water district boundaries.
19. When you have all the polygons you need (and have saved all your edits!), click the Editor dropdown and select Stop Editing.
1. In the ArcCatalog window, right click on Spartanburg.gdb.
2. Select Import > Feature Class (single).
3. In the dialog window, set the Input Features dropdown to WaterDistricts.
4. If not already selected, set the Output Location to Spartanburg.gdb. (On my computer, the path is D:\LadnerCI\Spartanburg.gdb)
5. Set the Output Feature Class to WaterDistricts.
6. Click OK to run the tool. The new feature class is added to the map.
Exporting a feature class is a similar process.
7. In the ArcCatalog window, right click on the WaterDistricts feature class in Spartanburg.gdb.
8. Select Export > To Shapefile (single).
9. Set the Output Location to the LadnerCI folder (e.g. D:\LadnerCI).
10. Save the Output Feature Class as WaterDistrictsExp.
11. Click OK to run the tool.
The resulting shapefile is identical to our original shapefile, with the exception that the perimeter and area of the polygon are preserved in the attribute table.
