EXERCISE 3A-3D
MAKING SPATIAL DATA USABLE
FOR/GGR 525

BE SURE TO SAVE YOUR WORK REGULARLY!!!

  When editing a layer in ArcMap, make sure you use the Save Edits option on the Editor toolbar to save edits as a separate process from saving your map.

INTRODUCTION

In this set of exercises (3A, 3B, 3C, 3D), you will:

  1. look at the setup of your coverage;
  2. identify errors made while digitizing;
  3. fix the errors and reconstruct the topology; and
  4. learn additional ArcMap capabilities.

EXERCISE 3A
CONSTRUCT TOPOLOGY

INSTRUCTIONS FOR COMPLETING THE EXERCISE

  1. Initial login.
  1. Logon to the workstation.

  2. In Windows Explorer, locate the net coverage you digitized in Exercise 2.

  3. Double-click the coverage name and look at the files in this folder (coverage).

  4. Remember that a coverage is really just a folder with files inside it.
  1. Use ArcCatalog to look at information about the digitized coverage.
  1. Highlight the Contents tab.

    You should see the different types of 'layers' associated with the coverage. A polygon coverage should have four layers associated with it: arc, label, polygon and tic layers.

  2. Double-click each layer and look at at each of the tabs (General, Items, and Relationships). Note the number of features in each and the items, or fields, in each associated table. Click Cancel when you are finished looking at each layer and property.

 

  1. Now click on fwsenet again and then select the Preview tab.

    Look at both Geography and Table. Geography should show you a 'sketch' of the coverage features. Notice what does the table view looks like. Also notice that in the Geography view, features in the polygon layer may be missing.

  2. Click on the polygon layer (fwsenet polygon) in the catalog window.

    Notice that the table changes. You can view each one of the tables from Preview/Table that you previously accessed by double-clicking each layer.

  3. Next click on the Metadata tab.

    Look through all the options for describing spatial data in ArcInfo under each tab: Description, Spatial, and Attributes.
  1. Get information about the coverage topology.
  1. Right mouse-click fwsenet in the ArcCatalog window.

  2. Choose Properties to see the topology.

    Topology is what determines the relationships between features, i.e. which arcs makes polygons, which polygons are adjacent to one another. In ArcInfo 8 (ArcGIS) when you digitize a coverage, the topology is automatically 'built.' However, it is important to know how to find out whether topology exists and how to update topology if needed.



  3. Look at the other information associated with the coverage from Properties using the other tabs: Projection, Tics and Extent, and Tolerances. Notice that you can define the coverage projection here under Projection. You can add, delete, and update tics (ground control points) from Tics and Extent, and search tolerances for editing can be set for the coverage under Tolerances. Note in the figure above that Topology exists for polygon feature class (layer) and preliminary topology is built for the arc feature class. All the feature classes have tables associated with them. If your arcs or labels are missing topology or a feature attribute table, you need to know how to build or rebuild it.
  1. Before constructing topology, first make a copy of your initial digitized coverage to be used in processing. Should problems arise in the initial processing, you will still have your original digitized coverage as a backup.
  1. In ArcCatalog, highlight fwsenet, right mouse-click, and select Copy.

  2. In ArcCatalog, right mouse-click tutorial and select Paste.

  3. Rename the new coverage fwsenetbu by right mouse-clicking the name (fwsenetcopy) and choosing Rename.
  1. Construct topology (relationships between the geographic features) for the fwsenetbu coverage.
  1. In ArcCatalog, right mouse-click the coverage and choose Properties.

  2. In the Coverage Properties window choose the General tab.

  3. Highlight the feature layer for which you desire to build topology.

  4. Click Build.

  5. Return to the Coverage Properties window and capture the Coverage Properties to print and hand in.

          The coverage fwsenetbu now has the desired topology (although it probably had it previously) and the accompanying polygon layer (fwsenetbu polygon).

  1. Read the paragraph below on BUILD vs. CLEAN, then go on to Exercise 3B.

_________________________

BUILD vs. CLEAN

To construct topology and create feature attribute tables you can use either BUILD or CLEAN. They differ somewhat. The major difference is that CLEAN uses a fuzzy tolerance to actually move or change features whereas build only develops the topology (relationships between features). Hence, BUILD cannot create intersections, whereas CLEAN creates intersections wherever lines cross one another (places nodes at intersections). In addition, CLEAN can correct undershoots and overshoots (dangles) as specified, so after major editing on lines or polygons use CLEAN, or when it is known that lines have been added without intersections being broken. Because CLEAN makes generalizations, it should be avoided whenever possible. See Table 1 below for a list of differences..

Table 1. Build versus Clean.

Capabilities/Processes BUILD CLEAN
PolygonsYesYes
LinesYesYes
PointsYesNo
Numbers featuresYesYes
Calculates spatial measurementsYesYes
Creates intersectionsNoYes
Processing speedFasterSlower

EXERCISE 3B
CHECKING FOR ERRORS

INTRODUCTION

The purpose of this exercise is to check for coverage errors, which should be done after you've created the initial topology for your fwsenet (now fwsenetbu) coverage.

INSTRUCTIONS FOR COMPLETING THE EXERCISE

  1. Open ArcMap. Look up "Reshape lines and polygons" in ArcGIS Desktop help for correcting digitizing errors. Using these tools to fix polygon errors will automatically update topological relationships.

    For example, if you have an arc splitting your polygon, you can activate the polygon layer, select the common arc, be sure that the Shared Edit tool is active, and delete the arc. However, using this technique, you will also have to eliminate the extra label. If you use topological tools to reshape the polygon instead (in the polygon layer), the label will be removed automatically. For example, use Merge to eliminate a common Arc between two polygons to create one polygon.

    Some of these functions only worked with Geodatabase layers at ArcInfo 8.0. However, ArcInfo 8 does not perform topological overlays on anything but coverages yet, so for a short period of time we will have to 'trick' the system into doing what we want. We are now using ArcInfo 8.1 (ArcGIS), which is supposed to fix some of these bugs. We will see...


     

  2. Download the ESRI white paper, 'Guide to Editing Coverages in ArcMap' at 'http://arconline.esri.com/arconline/whitepapers/ao_/ArcMapEditCov.pdf?PID=1.' Information specific to editing coverage topology is covered in this document.  Read it thoroughly.

 

EXERCISE 3C
USING ArcMap TO EDIT COVERAGE FEATURES

INTRODUCTION

Once the spatial errors have been identified, they can be corrected with ArcMap using the following general steps:

INSTRUCTIONS FOR COMPLETING THE EXERCISE

  1. Start ArcMap and either open a new map  or open the map you made previously.
  2. Add the fwsenetbu coverage, and make a copy of your coverage for editing, calling the new coverage fwseneted.
  1. In ArcCatalog, highlight fwsenetbu.

  2. Right mouse-click, select Copy.

  3. In ArcCatalog, right mouse-click, select Paste, type the new name, fwseneted.

  4. To add the fwseneted coverage-polygon layer to ArcMap, click on the Add Data button.

  5. When the browse window pops up, double-click fwseneted coverage to see the layers, and then double-click the polygon layer.

  6. Click on Editor to activate the drop-down window, and choose Start Editing.

  7. Be sure the Target is fwseneted polygon.

  8. Click Editor and choose Snapping...

  9. Check the features you wish to snap.
  1. Choose an option for editing.
  1. Look at the options for editing features, read about the function of each in Help, and then choose the appropriate method depending on what you need to edit. Be sure to select the shared edit tool if the features you are editing are shared by other features, like boundaries of polygons (which are shared by two polygons).

  2. Click on Task/Create New Feature, Task/AutoComplete Polygon, Task/Select Features Using a Line,
    etc...

  3. Select Help/ArcMap Help

3.  Select and edit the feature.

  1. Using the mouse cursor and left mouse button, point to the features to select. 

    Subsequent editing only takes place on the selected set of features. For some actions you can only edit one feature (e.g., an individual arc) at a time; for all actions you can only edit one feature type or layer (e.g. arc or polygon) at a time.

  2. Use the Shared Edit tool to select an arc to edit.

    If you are editing arcs not part of polygons, or points, you can use the edit tool  . However, since you are editing arcs making up polygons, you must use the shared edit tool .

  3. Delete the selected feature by hitting the Delete key on the keyboard.

  4. To bring it back use Ctr-Z.

  5. Add verticies to reshape feature. The following instructions come directly from ArcMap Help.

    1. Click the Current Task dropdown arrow and click Modify Feature.

    2. Click the Shared Edit tool and click on the line or polygon to which you add a vertex.

    3. Move the pointer to where you want the vertex added and right-click.

    4. Click Insert Vertex. A vertex is added to the sketch.

    5. When finished modifiying the line, right-click and choose Finish Sketch.

    6. This might be a good time to save your work.


    You can add vertices to a feature from the last vertex of the sketch. Click the Edit tool and double-click the feature to see its sketch. Then click the Sketch tool to begin digitizing vertices.

  6. Now use ArcMap to fix label errors.

    1. Add the fwseneted label layer to ArcMap.

    2. Select any extra labels (like the ones you may have in the lower portion of the coverage) and delete them using the Delete key on the keyboard. Don't delete labels inside of polygons (you can't anyway, hopefully).
  7. 'Play around' with some of these editing features.

4.  If appropriate, Save the changes made to the coverage by clicking on Editor/Save Edits. Exit ArcMap.

      If your coverage was correct, you do not have to save it.

5.  When you make changes to your coverage you should check/rebuild the topology.

    1. In ArcCatalog right mouse-click on the coverage and choose Properties.

    2. Select the General tab, highlight the polygon row, and click Build.

6.   Exit ArcCatalog and logout.

       You may skip this Step and Step 1 below if you choose to complete Exercise 3D during this session.

EXERCISE 3D
ADDITIONAL EDITING TOOLS

INTRODUCTION

The purpose of this exercise is to gain additional experience with ArcMap. You will need a coverage with polygon topology named fwseneted in your workspace. 

INSTRUCTIONS FOR COMPLETING THE EXERCISE.

  1. Logon to the computer, and start ArcCatalog.

  2. Make a copy of your coverage for editing, called fwseneted2 and initiate ArcMap.

  3. Open either a new map or one you made previously.

  4. Add the fwseneted2 polygon, arc and label layers to ArcMap.

  5. Start editing.

  6. Specify some snap environment settings.

  7. Look at all the available Tasks in the Editor Toolbar. 



  8. Practice any or all of the following tasks on your fwseneted2 coverage (that could be any layer). When clicking the edit tool, be sure to choose the proper tool depending on whether you edit shared or unshared features.
    Select features using a line.
    1. Click the Current Task dropdown arrow and click Select Features Using a Line.
    2. Click the tool palette dropdown arrow and click the Sketch tool or any of the other construction tools in the tool palette.
    3. Construct a line that intersects the features you want to select. The features that the line intersects are now selected.

    Select features using a polygon.

    1. Click the Current Task dropdown arrow and click Select Features Using an Area.
    2. Click the tool palette dropdown arrow and click the Sketch tool or any of the other construction tools in the tool palette.
    3. Construct a polygon that intersects the features you want to select. The features that intersect with the polygon you created are now selected

    Extend/Trim Lines
    Extend lines: The Extend task extends selected lines to a line you construct.

    1. Click the Current Task dropdown arrow and click Extend/Trim Features.
    2. Click the Edit tool .
    3. Click the line to extend.
    4. Click the tool palette dropdown arrow and click the Sketch tool .
    5. Construct a line to where you want to extend the selected line.
    6. Right-click anywhere on the feature and click Finish Sketch. The lines are extended to the line you constructed.

      You can also use the Distance-Distance tool, the Arc tool, or the Intersection tool to create a sketch. For more information, see ‘ Creating new features’ under ‘The ArcMap Editor’ in the Help Contents. You can double-click on the last vertex of a sketch to finish it. Or you can press F2.

    Trim using a sketch

    1. Click the Current Task dropdown arrow and click Extend/Trim Features.
    2. Click the Edit tool .
    3. Click the line you want to trim.
    4. Click the tool palette dropdown arrow and click the Sketch tool .
    5. Construct a line to indicate where the selected line will be trimmed.
    6. Right-click anywhere on the feature and click Finish Sketch. The lines are trimmed on the right side of the line you constructed.

    Mirror features: The Mirror task creates a mirror image of selected features on the other side of a line you create. For example, you can create houses in a housing development where houses are mirror images of the ones on the oppositie side of the street.
    1. Click the Edit tool .
    2. Click the feature that you want to mirror.
    3. Click the Current Task dropdown arrow and click Mirror Features.
    4. Click the tool palette dropdown arrow and click the Sketch tool.
    5. Construct a line by clicking once on the startpoint and once on the endpoint. After you digitize the endpoint, a mirror image of the feature is created.

      Don't fret if this tool doesn't work; it is rather buggy. On the other hand, if you do get it to work, show your lab instructor and you will receive extra credit.

    Modify or Reshape features

    Move vertices: Moving a vertex in a sketch offers another way to modify or reshape a feature. With the Editor you can move a vertex in several ways: by dragging it, specifying new x,y coordinates, or moving it relative to its current location.

    1. Drag a vertex
      1 Click the Current Task dropdown arrow and click Modify Feature.
      2 Click the Edit tool and click the line or polygon whose vertex you want to move.
      3 Position the pointer over the vertex you want to move until the pointer changes.
      4 Click and drag the vertex to the desired location.
      5 Right-click over the modified feature and click Finish Sketch. The feature is reshaped.
    2. Move a vertex by specifying x,y coordinates
      1 Click the Current Task dropdown arrow and click Modify Feature.
      2 Click the Edit tool and click the line or polygon whose vertex you want to move.
      3 Position the pointer over the vertex you want to move until the pointer changes.
      4 Right-click and click Move To.
      5 Type the x,y coordinates where you want to move the vertex. The vertex is moved.
      6 Right-click over the feature and click Finish Sketch. The feature is reshaped.

      You can also move a vertex without changing the shape of the feature. For more information, see Stretch a feature's geometry. To undo a vertex move, click the Undo button on the ArcMap Standard toolbar. The vertex returns to its last position. Click the Redo button if you want to move the vertex back to the new location.
    3. Move a vertex relative to its current location
      1 Click the Current Task dropdown arrow and click Modify Feature.
      2 Click the Edit tool and click the line or polygon whose vertex you want to move.
      3 Position the pointer over the vertex you want to move until the pointer changes.
      4 Right-click and click Move.
      5 Type the delta x,y coordinates where you want to move the vertex. The vertex is moved.
      6 Right-click over the modified feature and click Finish Sketch. The feature is reshaped.

    Add a vertex
    1 Click the Current Task dropdown arrow and click Modify Feature.
    2 Click the Edit tool and click on the line or polygon to which you want to add a vertex.
    3 Move the pointer to where you want the vertex added and right-click.
    4 Click Insert Vertex. A vertex is added to the sketch.
    5 When finished modifiying the line, right-click over the modified feature and click Finish Sketch.

    You can add vertices to a feature from the last vertex of the sketch. Click the Edit tool and double-click the feature to see its sketch. Then click the Sketch tool to begin digitizing vertices. To "re-add" an arc (deleted by accident), you can type Ctrl-Z  which "undoes" edits step-by-step, starting with the last edit made and extending back to the last time you saved the map document.

  9. Save your changes.

  10. Create a layout showing the changes you have made in your polygon and line coverages. Add text to the layout naming what tools were used to do which changes. Turn in the layout to your TA.  

  11. Exit ArcMap.

  12. Build or clean your edited coverage in ArcCatalog.

  13. Exit ArcCatalog.

  14. Logout

Return Return to Class Home Page...