Lab 5: Heads-up Digitizing into a Geodatabase, Part II

5.0 Summary of Part I (Lab 4)

In Lab 4 you created a database, a feature dataset and a feature class that now contain nearly all of the elements of your map.  What is lacking is a "Rock Units" feature class, with polygons that can be filled with colors/patterns to symbolize the geological units.  In the final steps of Lab 4, you digitized the outline of the rock units, stored the results in a GeoLines_XXX (alias "Contacts and Faults" ) feature class and created a topology.  With topology rules you specified that lines can not overlap  or cross ("intersect") other lines or themselves, and that they can not "dangle", i.e. starting and ending vertices of such lines must be precisely coincident with other lines.

By "validating" the topology, you had the software find all of the places on your map where the rules are broken.  These places are now marked so that they can be fixed by editing with special tools, which are explained below.  Such editing is essential if we want the software to create the rock unit polygons correctly, without errors.  Before starting, make copies of your GeoLines_XXX feature class using ArcCatalog.  Name the copies with a "2" or "3" at the end of the file name and store them in the Geology feature dataset.  If editing goes badly, you can always start over with a fresh copy and new topology.

5.1 Fixing Topology Errors

Described below are automated and manual techniques for removing errors.  An error is a violation of a specific topology rule.  Dangle errors are where lines "undershoot" or "overshoot" a line they where supposed to meet.  Such errors are classified as "Point Errors" for display, because they can be fixed by moving or eliminating one (or a few) vertices.   Intersection errors are where a single line loops back and crosses itself before continuing on.  These are also classified as point errors.  Overlap errors are where lines (or parts of lines) were accidentally digitized twice.  These are classified as "Line Errors" and display as pink lines.

ArcGIS Help on these subjects can be found by searching "Finding Topology Errors", "About Fixing Topology Errors" and "Fixing Topology Errors".  Some of the same material is covered in "Chapter 4: Editing Topology" in "Editing in ArcMap" in the digital books folder. 

1. Open ArcMap with a new, empty document.

2. Load the "Geology_Topology" feature class.  Answer "Yes" to the question, which then adds the GeoLines_XXX feature class. 

With the exception of the "Contacts and Faults" symbology, your map should display errors like the one below with, of course, different errors.

The map above shows one "Line Error" (pink line near river bend), where a contact (or part of a contact) was accidentally digitized twice, and four "Point Errors" where dangles or self intersections exist.  These are the errors in the Summary at the end of Lab 4.   Let's fix the errors.

3. If not already turned on, turn on the Editing toolbar (click the button that does so on the ArcMap standard toolbar)

4. Turn on the Topology toolbar (Customize>Toolbars>Topology, check the Topology box)

5. "Start Editing" (from the Editor toolbar drop-down menu choose "Start Editing")

6. On the Topology toolbar, click the "Select Topology" button , choose "Geodatabase_Topology"

7. Open the "Error Inspector" window by clicking on the Error Inspector tool .  Populate the window by clicking "Search Now" to see the errors listed, as below.
   

We want to use automated tools to fix as many of the errors as possible.  To do so, we will use the "Fix Topology Error" tool .

8. Click the "Fix Topology Error" tool .  The cursor changes to look like that on the tool button.

1. To fix a (poly)Line Error (pink line):

• click the line error with the Fix Topology Error tool; the color of the line changes from pink to black.  The error now appears in the Error Inspector, which shows the rule being violated (i.e. "Must Not Overlap") and other information about the line feature.  Overlapping lines errors can be fixed by "subtracting" one of the lines away.

• Right-click on a now black (selected) line or right click on the listed error in the Error Inspector and select "Subtract".   A Subtract window opens.

• In the Subtract window, choose the line from which the error will be subtracted (you can see which line is which by clicking on the line number in the Subtract window; the line is briefly highlighted on the screen) and click OK.  This removes the duplicate line, or the portion of the line that overlaps another line feature.  Be careful - don't delete the wrong line!

• You can undo individual changes by typing Ctrl-Z or by using the Undo tool on the ArcMap standard toolbar.

• To check your fix, click the "Validate Topology in Current Extent" tool .

• SAVE EDITS

2. To fix a Point Error (pink square:)

There are two types of Point Errors: Dangle errors and Self Intersect errors.  We will deal with Dangle errors first, of which there are two types; 1) those where a line was suppose to meet another line and 2) those where the line was suppose to close on itself (have coincident starting and ending vertices).  Before we do so consider that some dangles may be permitted, for example lines for faults are permitted to extend beyond where they meet another line.  So, before fixing any dangle errors, look at the screen and identify dangle error that are not, in fact, error and mark them as "Exceptions" in the Error Inspector".  This also can be done with a right click on the pink dangle error indicator.

1. To fix a Dangle error where a line was suppose to meet another line (as in the figure below):
   We first need to know whether the dangle is an "undershoot" and the line needs to be "extended" (as shown below), or whether it is an "overshoot" and needs to be "trimmed".

• To determine whether a line needs to be trimmed or extended, right-click the pink point error in question and select "Zoom to", then right-click on "Layers" in the TOC and select "Reference Scale">Set Reference Scale.

• To extend or trim, right-click the now black square (the once pink error marker), select either "Extend..." or Trim...", and type in a maximum distance (in meters) between the line and the feature you want it to meet.  If your first attempt doesn't work, try again with a longer distance.

• Another (but less predictable) way to fix such errors is to select "Snap..." from the right-click menu and then give a distance to the nearest line feature you wish to snap to.  If no line is found within that distance, no snapping occurs; try again with a longer distance.   "Snap..." will not snap dangle errors to an end of the same feature (see below for such fixes), only to a different line feature in the same feature class.  It searches first for an endpoint to snap to; if none is found within the distance it searches for vertices, and then finally for the nearest line.

• To check your fix, click the "Validate Topology in Current Extent" tool .

• You can undo individual changes by typing Ctrl-Z or by using the Undo tool on the ArcMap standard toolbar.

• If you zoom out and the pink errors no longer show, reset the Reference Scale, as described above.

• SAVE EDITS.

2. To fix a Dangle error where a line was suppose to close on itself (as in the figure below):
   The "Extend...", "Trim..." and "Snap..." tools will not work in these cases and the Dangle error must be fixed manually.

• If not already set, turn on "Vertex" and "End" snapping (Snapping toolbar).

• On the Topology toolbar click the Topology Edit tool .

• With the Topology Edit tool selected, click the line you wish to fix (not the pink error marker, but the line that includes it).  The vertices on the line should now appear as green squares, and the end node as a red square, as in the figure below.

• Move the cursor to the end node (red square); it changes from an open arrowhead to an open square with 4 enclosing black arrowheads when directly over the node.

• With the cursor now changed to the open square shape, left-click, hold and drag the red node to the beginning of the line, where it should snap to a green vertex.  Release the click.

• You can undo individual changes by typing Ctrl-Z or by using the Undo tool on the ArcMap standard toolbar.

• If you zoom out and the pink errors no longer show, reset the Reference Scale, as described above.

• SAVE EDITS.

• To check your fix, click the "Validate Topology in Current Extent" tool .

3. To fix a Self Intersect point error (shown below):

• click the error with the Fix Topology Error tool; the color of the point changes from pink to black.

• Right-click the now black (once pink) point and select "Simplify", which removes self overlapping line segments.

• If this does not work (e.g. the Simplify tool is unavailable), move the vertices in the area of intersection to remove the self intersection using the techniques described above in fix 2.

• You can undo individual changes by typing Ctrl-Z or by using the Undo tool on the ArcMap standard toolbar.

• To check your fix, click the "Validate Topology in Current Extent" tool .

• If you zoom out and the pink errors no longer show, reset the Reference Scale, as described above.

• SAVE EDITS.

Once you've made fixes, you can "Validate" the topology again to see if the fixes worked.  Two tools on the Topology toolbar are there to do so; the icons with black check marks.  Using these tools, you can validate within a specified area or within the "current extent" (the area visible on the screen).

9. Work your way through the errors, one-by-one, fixing them all.

10. Validate the topology as you go, until no errors are left.  An easy way to check for remaining errors is to click the "Search Now" button in the Error Inspector, with only the "Errors" box checked and the "Show:" field set to "<Errors from all rules>", as shown below (with no remaining errors!).

11. SAVE EDITS.

12. "Stop Editing" (Editor Toolbar drop-down menu, "Stop Editing").

13. Ensure that you have fixed all topology errors before proceeding by Zooming to the Geology_Topology layer to see a screen free of any pink boxes or lines!

5.2 Making Rock Unit Polygons

Once all topology errors are fixed, Rock Unit polygons can be generated.

1. If not already open, open ArcToolbox from within ArcMap using the button in the Main toolbar.

2. Open the "Data Management" toolbox in ArcToolbox and find the "Feature to Polygon Tool" (Use the Search window. Forget how?  See the Lab 1 section on this topic).  If not already on, turn on the "Show Help" at the bottom of the tool.

3. The "Input Features" for our new Rock Unit polygons is the Contacts and Faults(GeolinesXXX) feature class, the cluster tolerance is 0.001 meter and the Output should be saved to the Geology Feature Dataset with the name Rock_Units_XXX, where XXX is your initials.

4. Click OK.  The new Rock_Units_XXX polygon feature class is created (shown below).  Not surprisingly, this looks just like GeoLines_XXX feature class except for the purple background, indicating these are polygons, not lines.

5.3 Creating Rock Unit Attribute Fields and Assigning Domains

To symbolize and label rock units, two additional fields are required, for which we have already created domains.

• Using the procedures in Lab 4, create two new text fields named "Name" and "Abbrev" for the Rock_Units_XXX feature class.  This does not require a new feature, simply a new field within the existing feature class.  These can be created either in ArcCatalog, as in Lab 4, or alternatively in ArcMap by opening the attribute table and choosing "Table Options" from the icons at the top of the attribute table window. The "Name" field should have Length of 50 and use the "Unit_Name" domain; the "Abbrev" field should have a Length of 5 and use the "Unit_Abbrev" domain.

5.4 Assigning Attributes to the Rock Unit Polygons

1. Open an empty ArcMap document and add the GeoLines_XXX and Rock_Units_XXX feature classes.

2. Add the rectified geologic map scan and move it to the bottom of the table of contents.

3. Symbolize the Rock_Units_XXX polygons with "No Color" so you can see the geologic map beneath them.

4. Set the Selectable layers to Rock_Units only (turn off selectability for all others).

5. From the Editor toolbar, Start Editing; In the Create Feature window select Rock_Units_XXX; click the arrowhead tool (on the Editor toolbar) and click a polygon on the map to select it.  Alternatively, open the Attribute table and select a record, Zoom to Selected (with a right-click), and then assign the Name and abbrev from the drop-down list.

6. SAVE EDITS frequently.

7. When you think you have attributed all of the polygons, open the attribute table for Rock_Units_XXX and check.  The Name and Abbrev field for all features should not contain any <null> values.  If one does, select the record that contains the null value (click it), "Zoom to Selected" (from a right-click on Rock_Units in the table of contents; can also be done by a double-click on the row in the table), zoom out, and attribute the polygon.

8. When finished Save Edits and Stop Editing.

Congratulations, you have now finished creating/editing the geology feature classes needed for the geologic map!

10. To symbolize the rock units with patterns and fills that closely match the original map, use the "Styles" available in the Lab_4_data folder.  These can be accessed through the Rock_Units_XXX Symbology tab and Symbol Selector.  Note the "Style References..." button on the Symbol Selector, from which one can "Add Style to List...".  Experiment and/or use the Help files see if you can't figure out how.  There are pre-made colors/patterns for all units.  Importantly, these will have to be altered to show "no color" for the outlines so that the dashed and solid geolines can be used for rock unit outlines (contacts) instead.  Pro tip:  if you created your own elaborate symbol or fill, save it to a Style so it can be used again.

5.5 Clipping Feature Classes to the Map Boundary

1. If not already open, open ArcToolbox from within ArcMap.

2. Expand the "Analysis" toolbox, then the "Extract" toolbox to see the "Clip" tool.

3. Open the Clip tool.

4. Click the folder button next to the "Input Features" field, browse to your geodatabase and double-click on contours_5m feature class.

5. Click the folder button next to the "Clip Features" field, browse to  your geodatabase and double-click on the Area_of_Interest feature class.

6. Name the new file in the "Output Feature Class" field, and click OK.  A new feature class of contours that are clipped to the map area has been created!  Add them to the map and symbolize using the instructions below.

7. Repeat steps 3 - 6 for any of the other base map feature classes needing to be clipped, providing new names if you wish.

5.6 Symbolizing Streams, Lakes and Contour Feature Classes; Labeling Index Contours

1. ArcMap contains ready-made symbols for many feature classes - use them for the streams, lakes and roads.

2. To symbolize the 100, 125, 150 and 175 meter contours with a thicker line (as is the custom on topographic maps; these are called "Index" contours):

   1. Symbolize the Contour feature class by Categories;

   2. Change the "Value Field" to "Contour";

   3.  "Add Values" of 100, 125, 150 and 175;

   4. Symbolize these categories with the "Contour, Topographic, Index" symbol;

   5. Change the "all other values" symbol to "Contour, Topographic, Intermediate".  The result is shown below.

4. Give all feature classes simple new Layer Names in the Table of Contents (use the "General" tab in the layer's Property window) that would make sense in a legend.

5. To label the Index contours, you'll need to make a new Label Class (call it "Index"), and construct an SQL query that limits the Class to where "Contour" is equal to the Index contour values.  See Lab 3 if you've forgotten how.  The labels should be 10 point, Arial italic with the same color as the contours, with a 1 point light brown "halo", and a Placement that allows curving to follow contours lines.  Use the Maplex label engine for best results.

5.7 Symbolizing and Labeling the Remaining Layers

The remaining layers should be symbolized and labeled by the Domain values we entered, e.g. "Exposure" (dashed versus solid line versus dotted) and "Abbrev" for rock unit labels.

1. Symbolize Rock Units without an outline and with a color/pattern scheme from the GAT style sheets in the Lab_4_data folder or of colors of your own choosing. Use your GeoLines_XXX feature class, properly symbolized, for rock unit outline (contacts). A few examples are shown below.

2. Label Rock Units with Abbreviations. Convert dynamic labels to annotations (see Lab 3) as need for the best placements.

Questions:
1) What percentage of the map area is underlain by Reklaw Formation?  By the Calvert Bluff Formation?

2) What is the area of the map; how much ground do we have to cover during our field trip?

3) What are the highest and lowest elevations of the high gravels?

4) How deeply incised is the Colorado River in this area?

To turn in:  A polished, landscape-or portrait-mode layout, with a legend, title, etc.  See Maps of the Week (some not so good) and the partially completed maps below for some examples.  Note the use of partial transparency and the order of the layers (what lies on top of what) in the examples below.