GEOG 4813:  GIS      
Building Your Own Geodatabase Using ArcGIS

Part 2:  On-screen digitizing of spatial features in a geodatabase using ArcMap

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Part 2 of this tutorial assumes that you have already completed Part 1 (it can be accessed at <http://arapaho.nsuok.edu/~ziehr/courses/geog4813/Building_Your_Own_Geodatabase_Using_ArcGIS-Part1.html>). This tutorial  is designed to lead you through the process of on-screen digitizing of spatial features into a newly-created personal geodatabase using ArcMap.  It is assumed that you've already studied Chapter 15 which gives instructions for on-screen (or "heads-up") digitizing in "Getting to Know ArcGIS Desktop".  We'll use a DOQQ of Tahlequah (specifically i:/ziehr/Exercise4/35094h83.bil) as our source reference for on-screen digitizing.  There are a lot of steps involved, but follow along carefully and think conceptually and you'll be successful.  We start with step 19, where Part 1 left off.

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19. Launch ArcMap.
20. Add your DOQQ to a new map (i:/ziehr/Exercise4/35094h83.bil).
    
    
    
    
21. Right-click on the Data Frame (Layers) and choose Properties.  In the Data Frame Properties box click the Coordinates tab.
    
    
    
    
22. Select a coordinate system by double-clicking on Predefined; then double-click on Projected Coordinate Systems and then on Utm and then on Nad 1983.  Highlight NAD 1983 UTM Zone 15N and press OK.
    
    
    
    
23. Using "Add Data" navigate to the folder that contains your newly-created personal geodatabase, highlight it, and press Add.
    
    
    
    
24. Then highlight the feature class of your choice, such as "Streets" and press Add.
    
    
    
    
25. The Streets datafile has been added to the Layers data frame.
    
    
    
    
26. Press the down arrow by Editor and choose Start Editing.
    
    
    
    
    
27. Notice that the Task: box on the Editor bar now defaults to "Create New Feature", which is what you want to do.  The Target: box lists the first (and in my case only) Feature Class (Streets) in my personal geodatabase.  If you have more than one Feature Class specified (which you will have to for the homework exercise), click the down area and select the Feature Class that you wish to edit.  Zoom to an area of town in which you wish to begin on-screen digitizing of a Street line feature (for example the Crafton Street area).
    
    
    
    
28. Click the down-arrow by Editor and select Options.
    
    
    
    
29. Be sure you've studied the Exercise 15a tutorial in the "Getting to Know ArcGIS Desktop" book, especially the portion about the Snapping Environment.  Give particular attention to page 384 and Editing in ArcMap > Creating new features > Using the snapping environment in the ArcGIS Desktop Help.
    
    
    
    
30. In the Editing Options box click the General tab and set the Snapping tolerance in map units (map units for our DOQQ are in meters).
    
    
    
    
31. Click Editor and select Snapping.
    
    
    
    
32. Check Vertex in the Street Layer.  This will allow streets that intersect with other streets to snap to existing street vertices.  This helps prevent overshooting and undershooting while digitizing.
    
    
    
    
33. Click the "x" in the upper right hand corner of the Snapping Environment box, and you're ready to begin digitizing.
    
     
    
    
34. Click the Sketch Tool    on the Editor bar.
35. Click the cursor which is now the Sketch Tool at the end of the first spatial feature to be digitized (in our example, a street).  For example, I have placed the Sketch Tool cursor at the east end of Crafton Street.
    
    
    
    
36. Digitize the street by click each time the street changes direction (curves are approximated with a series of short straight lines) and at each intersection (without a vertex at each intersection you cannot snap an intersecting street into the correct position).
    
    
    
    
37. You may use the zoom tool to enlarge the image (to make sure you're digitizing the intended feature) even while you're still digitizing a line.  Once the image has zoomed in, once again click the Sketch Tool button, and you are able to resume digitizing exactly where you left off.
    
    
    
    
38. At the west end of Crafton Street (where it intersects with Grand Avenue), double-click the last vertex to end digitizing of that feature (Crafton Street).  The line that you've just digitizes changes to the "selected feature" color and the little boxes that indicated each vertex that you digitized are no longer visible.
    
    
    
    
39. You are now ready to digitize a second street.  Let's do Grand Avenue so that we can see the Snapping Environment in action.  Zoom to the north end of Grand Avenue, where it intersects the Bertha Parker By-Pass.  Grand Avenue proceeds south from that intersection to Valley Drive on the south (remember that Valley Drive is that short little curved section that joins Grand Avenue to Muskogee Avenue by the NSU Administration Building).  With the Sketch Tool begin digitizing Grand Avenue and proceed to click on vertices as you move toward the south.
    
    
    
    
40. Remember to zoom in as necessary and be sure to digitize a vertex at intersections.  
    
    
    
    
41. As you near the intersection with Crafton Street zoom in closely so that you can see the effect of snapping and the snapping tolerance.  
    
    
    
    
42. Move the cursor very slowly as you approach the Crafton intersection.  When you are within the snapping tolerance distance of a street vertex, you will see the cursor jump to the existing vertex.  In this case to the last vertex on the west end of Crafton Street.  Perhaps you'll remember that we set the snapping tolerance at 10 meters (see Step 30 above), so the cursor won't jump until you're within 10 meters of the vertex at the intersection.  When it does jump to the vertex click it so that the exact intersection becomes a part of Grand Avenue (it is already a part of Crafton Street).  This way the streets with intersect smoothly without an overshoot.  Continue digitizing to the end of Grand (where the street begins to curve and becomes Valley Drive); double-click the last vertex, and you've completed your second spatial feature.
    
    
    
    
43. Notice that Grand Avenue became the "selected feature" color and Crafton Street changed to the Street color in the legend (and is no longer selected).  While you are digitizing the last feature digitized remains selected.  When a feature is selected and your're still in editing mode, you can use Edit -- Undo to correct errors and start again.  Be sure to periodically Save Edits even if you want to keep editing.  You don't want to lose the work that you've done.  Click Editor and click on Save Edits.  [If you're ready to stop editing, of course, you would click on Stop Editing.]
    
    
    
    
44. We can now edit the attributes of our new spatial features.  In our example our spatial features are streets, and we created a field in our attribute table for Street_Name (Part 1, Step 16); so we need to enter the street names into our database.  Make sure you're in editing mode by clicking on Editor and selecting Start Editing.  Then click the Edit Tool    and use it to select one of your streets by moving the cursor over the street and clicking it.  The selected street will be turned to the "selected feature" color.  In our example we've selected Crafton Street.
    
    
    
    
45. Click the Attributes button near the end of the Editor bar.
    
    
    
    
46. With a feature selected when the Attribute button is pushed the Attributes box appears.  It displays the attributes of the selected spatial feature.  Notice that the Value of Street_Name is <Null> which means that cell is currently empty.  
    
    
    
    
47. Click on <Null> and type it the street's name; in this case that's Crafton Street.  Try clicking on the Value for OBJECTID and SHAPE_Length.  ArcMap will not allow these to be edited.  They are required and system-generated for each spatial feature.
    
    
    
    
48. With the Attributes box still open click the cursor on Grand Avenue in the on-screen image.  Grand Avenue now becomes selected, and its attributes are displayed in the Attributes box.  You can now click on <Null> and enter Grand Avenue for the Street_Name field.  Click the close buttion ("x") in the upper right hand corner of the Attributes box and then click Editor and select Stop Editing.  You'll be prompted with "Do you want to save your edits?"  reply by clicking Yes, and you've completed your personal geodatabase.
    
    
    
    
49. Save your Map Document (.mxd) so that you can return to this DOQQ and map of Tahlequah streets in the future.  Additional streets can be added to the Streets feature class in your personal geodatabase whenever you choose by opening the Map Document and going back into editing mode (via Editor).  If you want to add a new feature class to your geodatabase, such as the traffic signals (points) and neighborhoods (polygons) required in the homework exercise, go back into ArcCatalog.  Inside of ArcCatalog simply navigate to the folder containing your personal geodatabase and highlight it.  Then click File -- New -- Feature Class, and you're ready to begin (you're at Step 4 of Part 1 if you need to go back to the tutorial for review of the steps involved).
50. These have been rather "bare bones" instructions.  You should explore these techniques and capabilities in more detail.  In a real-world application (or even for the homework exercise) you would need to give considerable thought up-front before creating your geodatabase so that you could avoid as many problems as possible and so that you would not have to keep going back and adding and/or editing things that had been thought of in advance.  We'll practice this process of thinking about data design in class.
    

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    Last revised April 15, 2004.