Lab 6: Heads-up Digitizing into a Geodatabase, Part II

6.0 Summary of Part I (Lab 5)

In Lab 5 you created a database, a feature dataset and feature classes 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 5, you digitized the outline of the rock units, stored the results in the "Contacts" feature class and created a topology for the contacts and faults.  With topology rules you specified that contact lines can not overlap other contact lines or cross themselves, and that they can not "dangle", i.e. starting and ending vertices of such lines must be precisely coincident with other contact lines.  The same was true of fault lines, though they were permitted to dangle.  For future reference, we might have included two additional rules:

• "Must Not Self Overlap"; lines cannot overlap themselves.  This rules is different from rule we used ("Must Not Overlap"), which detects lines that overlap other lines in the same feature class.

• "Must Be Single Part"; our map does not have any "multipart" features (see Help files for an explanation of multipart features).

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 (in pink) so that they can be fixed by editing, which is 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 Contacts and Faults feature classes.  If editing goes badly, you can always start over with a fresh copy.

6.1 Fixing Topology Errors

Described below are automated 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.  For a more complete explanation of line topology rules (and their fixes) see "Chapter 4: Editing Topology" in "Editing in ArcMap".

1. Open ArcMap with a new, empty document.

2. Load the "Map_Area" feature class.

3. Load the "Contact_Topology" feature class.  Answer "Yes" to the question, which then adds the "Contacts" and "Faults" feature classes.

4. Set selectable layers to the Faults layer and Contacts layer (uncheck the Map_Area layer).

5. Right-click on "Layers" in the Table of Contents (in the figure below, "Layers" was renamed "Labs 5&6") and select Reference Scale>"Set Reference Scale". 

With the exception of the "Contacts" and "Faults" symbology, your map should look like the one below with, of course, different errors.  (Your map probably also shows a few small granite bodies that I left out.)

The map above shows 2 obvious Line Errors (pink lines; a third one is almost too small to see at this scale), where a contact (or part of a contact) was accidentally digitized twice, and 4 obvious Point Errors (pink squares; a fifth overlaps the eastern most error and is difficult to distinguish) where dangles or self intersections exist.  These are the errors in the Summary at the end of Lab 5.   Let's fix the errors.

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

7. Turn on the Topology toolbar (Tools>Customize, check the Topology box)

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

9. On the Topology toolbar, set the layer to "Contact_Topology" (choose from the drop-down menu)

10. On the Topology toolbar, click the Map topology tool .

    • The data that participate in the map topology are Faults and Contacts, but not Map_Area.  If "Map Area" is checked, uncheck the box next to it.  The "Cluster Tolerance" should be 15 meters.  Click OK.

11. If the layer indicated on the Topology toolbar changed after step 9, change it back to "Contact_Topology".

12. Open the "Error Inspector" window by clicking on the Error Inspector tool .

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 .

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

1. To fix a 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.

• 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 below.

• 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 a another line and 2) those where the line was suppose to close on itself (have coincident starting and ending vertices).

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 for the Contact layer (Editor toolbar; from the Editor drop-down menu choose "Snapping...", then check the boxes for "Vertex" and "End" for the Contact layer).

• On the Editor toolbar, set the Task to "Modify Edge".  This is found on the "Task:" drop-down menu, under "Topology Tasks" heading.

• 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.  Three 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, within the "current extent" (the area visible on the screen), or validate the entire topology.

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

15. 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!).

16. SAVE EDITS.

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

6.2 Making Rock Unit Polygons

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

1. Close ArcMap and open ArcCatalog (yes, you must close ArcMap; you can't work on the geodatabase in ArcCatalog if feature classes within it are open in ArcMap).

2. Go to the Castel_Map geodatabase and preview the Contact_Topology feature class.  The preview should reveal a blank screen; if not there are still errors that need to be fixed.  Fix them before proceeding.

3. Right-click on the Geology feature dataset and select "New", then select "Polygon Feature Class From Lines..."; the Polygon Feature Class From Lines window opens.

4. Name the new feature class "Rock_Units", specify a cluster tolerance of 1 meter, and put a check in the box adjacent to Contacts (the Contacts feature class is the only one that will contribute lines).

5. Click OK.  The  new Rock_Units polygon feature class is generated (shown below).  Not surprisingly, this looks just like Contacts feature class except for the yellow background, which indicates these are polygons, not simply lines.

6.3 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 (see lab 5).

• Using the procedures in Lab 5, create two new text fields named "Name" and "Abbrev" for the Rock_Unit feature class.  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.

6.4 Assigning Attributes to the Rock Unit Polygons

1. Open an empty ArcMap document and load all of the feature classes in the Geology feature dataset except "Contact_topology".

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

3. Symbolize the Rock_Unit 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, set the "Target:" to "Rock_Units", click the arrowhead tool (on the Editor toolbar) and click a polygon on the map to select it.

6. Using the procedures in Lab 5 and the rectified geologic map, assign Name and Abbrev attributes to the Rock Unit polygons.  On the rectified map, all unlabeled yellow areas are Quaternary Alluvium (Qal) and the brown areas are Undifferentiated Lower Paleozoic rocks (LPu).  All other colors/patterns are labeled.

7. SAVE EDITS frequently.

8. When you think you have attributed all of the polygons, open the attribute table for Rock_Units 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), zoom out, and attribute the polygon.

9. When finished Save Edits and Stop Editing.

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

6.5 Clipping The Roads, Contours, County Line And Stream Feature Classes With The Map Area Polygon

The stream, roads, county line and contour feature classes that we imported into the Castell geodatabase in Lab 5 have features that extend well beyond the boundary of the map area.  They need to be clipped to the Map_Area polygon so that the map will display and print only the area that was digitized.

1. From within ArcCatalog, open ArcToolbox by clicking the red toolbox icon.

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 the Castell_Map geodatabase and double-click on CastellandArt_contours feature class.

5. Click the folder button next to the "Clip Features" field, browse to the Castell_Map geodatabase>Geology feature dataset and double-click on the Map_Area feature class.

6. Accept the name and location of the new file that will be created, as indicated 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!

7. Repeat steps 3 - 6 for the NHD_streams_Llano, TX_county_lines, TXDOT_LlanoCo_Roads and TXDOT_Mason Co_Roads feature classes, providing new names if you wish.

8. Add the 5 new clipped files to ArcMap by dragging and dropping them from ArcCatalog, placing them above the Rock_Units layer in the table of contents.  Answer OK to any Warnings.

6.6 Joining A Look-up Table To The Roads Feature Classes

The Roads attribute tables contain fields that could be used to symbolize different road types (paved, county, state, federal, dirt, gravel, etc.) but the codes in these fields aren't intelligible.  To make them so, we will join them with a table that contains a code field (the "key field" for the join) and a description field that describes the meaning of each code.  Such a table is often referred to as a "look-up table", because it contains code descriptions.  The join we will do is referred to as a "many-to-many" join because many record in the look-up table are joined to many records in the destination table (see lecture notes).

1. Right-click on TXDOT_MasonCo_Roads_clip in the TOC, select "Joins and Relates", then "Join..." to bring up the Join Data window.

2. The field in the roads feature class that the join will be based on is "Level_" (item 1); the field in the look-up table that the join is based on is "Codes" (item 3).  Be sure you have selected the right table (item 2) and then click OK.

3. Answer "Yes" to create an index.

4. Repeat the process for the Llano county road feature class.

5. Examine the attribute table of one or both of the roads feature classes.  Notice that the table now contains three new fields, with bold capital letter headings,  at the far right from the look_up table: an OBJECTID, DESC_ and CODE field, with each field name preceded by the look-up table name you gave when importing this table in Lab 5.  We will the symbolize roads on the new DESC_ field.

6.7 Importing Road Symbology From A Layer File

A previously created layer file can be used to symbolize the roads.

1. Right-click on TXDOT_MasonCo_Roads_clip in the TOC, select "Propeties" and click the Symbology tab.

2. Click the "Import..." button to bring up Import Symbology window.

3. Using the folder button, browse to your Lab_5_data folder, open the "Roads" folder and double-click on the TXDOT_MasonCo_Roads layer file.

4. Click OK.

5. In the "Import Symbology Matching Dialog" window, change the value field to .DESC field (it will be preceded before the period by the look-up table name you gave in Lab 5).

6. Click OK, and the Layer Property Symbology tab appears, with symbols for the roads.

7. In the Layer Property Symbology window, click the word "Count" above the column with question marks.  The number of features in each symbol category is now shown, as illustrated below.

8. Right-click on the symbols for which the Count is 0 and select "Remove Value(s)".  This will eliminate them from displaying in a map legend and from the table of contents.

9. Change the Label for the <Heading> from "look_code2_DESC" to "Roads" by clicking on it and typing in the new name.

10. Using the same layer file, repeat steps 1-9 for the Llano roads feature class.

11. In the Layer Properties Window, change the Layer Names of the roads feature classes to Mason Co. Roads and Llano Co. Roads.

6.8 Symbolizing Streams, County Line, and Contour Feature Classes; Labeling Index Contours

1. ArcMap contains ready-made symbols for many of these feature classes.

2. Use the "River" symbol for streams and the "Boundary, County" for the county line.

3. To symbolize the 1200, 1300,1400 and 1500 feet contours with a thicker line (as is the custom on topographic maps; these are called "Index" contours), Symbolize the Contour feature class by Categories, Change the "Value Field" to "ELEV_FT" , "Add Values" of 1200, 1300,1400 and 1500 and symbolize these categories with the "Contour, Topographic, Index" symbol.  Change the "all other values" symbol to "Contour, Topographic, Intermediate".

4. Give each of these feature classes simple new Layer Names that would make sense in a legend.

5. To label the Index contours, you'll need to make a label class (call it "Index"), and construct an SQL query that limits the class to where "ELEV_FT" is equal to the Index contour values.  See Lab 4 for help.  The labels should be 8 point , Arial italic the same color as the contours, with a 1 point white "halo", allowed to curve to follow contours and placed on the lines.

6.9 Symbolizing And Labeling The Remaining Layers

The remaining layers should be symbolized by the categories we constructed fields for, e.g. Dike type, Exposure (dashed versus solid line), and rock unit name.

1. Symbolize Aplites with 2 point Tuscan Red lines, Marble lenses with 2 point Dark Navy lines.

2. Symbolize Faults with a 2 point black line.

3. Symbolize Contacts with a 0.4 black line.

4. Do not symbolize the Map Area boundary.

5. Symbolize towns, ranch houses and windmills differently, with symbols of your choosing.

6. Symbolize Rock Units without an outline (the contacts layer does the job) and with a color/pattern scheme that approximates that of the original (see the pitiful example below).

7. Label Rock Units with Abbreviations, the towns with names, and the windmills and ranch houses with "windmill" and "ranch".

8. Label the down-side of faults with a capital "D" and the up-side with a capital "U".

9. Label the major East-West highway (it's state Highway 29) with a highway shield containing the road number.

To turn in:  A polished, landscape-mode layout, with a legend, title, etc.  See Maps of the Week from last year for some examples.  An incomplete (and rather poorly symbolized) example is shown above.