p. 5.1: General Comments

The first bulleted list shows 6 items. Some of these concerns are addressed in advance in the notes for Lesson 4:

• All features that should have been digitized, really were (no missing data).
  You should check this by making sure that your DE settings were correct. If your DE settings show all features that you intended to add, you will be able to tell (during the digitizing process) if features have not been added. You can correct as you digitize.
  
  
• All features that are there, should be there (no extra data).
  Again, if your DE is set properly, you should be able to tell if this is the case.
  
  
• The features are in the right place and the arcs have the correct shape (data are accurate).
  You will be able to make this judgment by comparing with the map manuscript. If you used splining, the shape may be more true than if you did not.
  
  
• Features that connect, actually do.
  You should make sure that your DE was set to NODE ERRORS and your NODESNap and ARCSNap tolerances are set correctly when you digitize. If this is the case, there will be greater probability that features that should connect really do connect.
  
  
• All polygons have one, and only one, label point.
  If you used the CREATELABELS command to create labels, there is a chance that you may have duplicate labels for one polygon and no labels for another. This is because CREATELABELS puts label points in the centroids of polygons. In some cases, the centroid actually lies outside of a given polygon. For example, polygon #1 in this group will contain both label points:

The label point for polygon #2 will have to be moved inside the polygon boundary.

• All features are within the outer boundary.
  This is not an extremely critical constraint. You can always perform a REBOX on a coverage to reset the boundary to the extent of its spatial features.

p. 5.3-5: Identify digitizing errors

If you have digitized carefully, you will have fewer digitizing errors. Again, if you set your DE, NODESNap, and ARCSNap environments correctly, you will have less clean-up to do after your initial digitizing session. You will have fewer undershoots, overshoots, and open ("bleeding") polygons.

p. 5.10: BUILD vs. CLEAN

The text explains most of the differences between BUILD and CLEAN. There are a few more items to consider.

1. Because CLEAN has the option to remove dangling arcs, if you use this option, you must be careful to specify a tolerance that only removes unintentional dangles.
   
   
2. Because of the fuzzy tolerance option (the minimum distance between vertices in the CLEANed coverage) specified in CLEAN, some of your arcs may actually change shape. This is known as "fuzzy creep." If a coverage is CLEANed many times, its arcs may be shaped differently than the originally digitized coverage.
   
   
3. If you attempt to use BUILD on a coverage that has non-intersected crossing arcs, it will complain and fail. ARC will give you a message indicating the coordinate position of the first crossing. To print a list of all crossings, use the ARC command INTERSECTERRORS. You can then use this list in AE to create intersections.
   
   
   • To have intersections created automatically as you digitize, you can set the INTersectarcs environment to ADD or to ALL. In this case, when you add arcs that cross, intersections will automatically be created. Doing this can save steps later. However, if you make a mistake and add an arc in the wrong place and then delete it, any nodes that were created on existing arcs will remain. You can use the UNSPLIT command to remove unwanted pseudo-nodes.

p. 5.11: copying coverages

If you followed the instructions in the web notes for the introduction, you should have a copy of the RESULTS workspace in your UGIS directory. To copy the LANDDG01 cover to your LAND workspace, use the command

Arc: &wo c:/users/my_name/land
Arc: copy ..\results\landdg01 landdg01

or

Arc: &wo c:/users/my_name/results
Arc: copy landdg01 ..\land\landdg01

Do you see how these 2 command sequences are equivalent? The only difference is the location of the current working directory. In the first case, you are attached to the LAND workspace and you are copying from ../RESULTS, and in the second case, you are attached to the RESULTS workspace and are copying to ../LAND.

In either case, you must use the ARC command COPY. If you use the system command copy or xcopy, you will copy over the coverage directory, but you won't copy over the INFO tables associated with the coverage. If you use system commands to copy, you will have non-functional coverages.

p. 5.12: CLEAN vs. BUILD

Although you can certainly use CLEAN to force the creation of intersections, I recommend that you visually inspect the coverage at these intersections, and fix them within AE. As long as your intersection errors are really just spaghetti errors, CLEAN is not a bad option. However, if your error is more like this:

doing a clean will actually create an unintended polygon (the triangle). If you had inspected the intersection errors, you would have been able to find and correct this error. You could go ahead and perform a CLEAN and then later remove sliver polygons, but I recommend that you, rather than the ARC processor, maintain control over every stage of the creation of your coordinate data.

You can easily inspect intersection errors by copying and pasting the output of the INTERSECTERR command to a text editor such as notepad. Then, in AE, issue the commands:

APC MARKERCOLOR RED
APC MARKER <x1> <y1>
APC MARKER <x2> <y2>
...
APC MARKER <xn> <yn>

where the coordinate pairs are the "Intersection x" and "Intersection y" from the INTERSECTERR output. (The command APC is short for "ArcPlot Command." You can issue AP commands one at a time in AE, or you can run AP command AMLs by issuing the AP command, as long as you have an AML written.)

Use zoom windows to navigate to these intersections and fix them one by one. As you gain experience in digitizing, you will find that you have far fewer intersection errors.

p. 5.13: Removing dangling arcs

Be careful when you CLEAN with the dangle length option. You may actually remove dangling arcs that represent real features such as cul-de-sacs. My advice is to make sure you have no unintended dangles as you are digitizing. That way, you will not have to guess about the right dangle length in CLEAN.

p. 5.17-19: EDITPLOT

It is not necessary to perform an EDITPLOT every time you finish digitizing a coverage. EDITPLOT does not change your coverage in any way, but is simply an aid in locating possible digitizing errors. As your skills increase, you will be able to catch and fix errors as they happen. If you do perform many EDITPLOTs, you will have many unnecessary graphics files in your directories. To list these graphics files, you can issue the DOS command:

Arc: dir *.gra

You can remove these files one at a time or en masse by using the DOS command DELete.

To view your graphics file, issue the command:

Arc: &stat 9999; draw landcn.gra

Note the use of the semicolon, which allows you to place more than one command at the same prompt.

5.20: Hardcopy

We will cover hardcopy output in detail closer to the end of the workbook.

5.21: Watch files

A watch file is a simple ASCII file that copies the commands used and system responses generated between the &WATch <system_file> and the &WATch &OFF directives. You can view the file in any text editor or word processor, or you can use the &POPUP directive as described on p. 5.22.

You can actually send both the NODEERRORS and LABELERRORS (and INTERSECTERR, if you like) to the same watch file:

Arc: &watch digerr.txt
Arc: nodeerrors landcn all
Arc: labelerrors landcn
Arc: intersecterr landcn
Arc: &watch &off

p. 5.25: Labelerrors

In addition to simply listing label errors, you can also display label errors graphically. To do this, use ArcPlot:

Arc: ap
Arcplot: display 9999
Arcplot: mape landcn
Arcplot: arcs landcn
Arcplot: labelerrors landcn

Any polygons which have label errors will be shown with a symbol. In the case of polygons with more than one label point, these will display the label numbers. Polygons lacking a label point will have stars within them. There will always be a star in the very center of the coverage, corresponding to the non-existent label point for the universe polygon.

p. 5.30: Pan/Zoom menu

Instead of resetting the extent of the main AE display window, I suggest opening a new zoom window [(^W) Create] and setting its extent to the area you want to zoom into. This way, you will have an overview as well as a zoom window, as shown on p. 5.32.

In addition, you should commit to memory the keystrokes for the most common Pan/Zoom menu items. You will save time by typing ctrl-a instead of having to choose Pan from a pulldown menu.

p. 5.33: Selection color

You can choose any selection color you want by using the SetDrawSymbol command. SDS options include a symbol number and a color. For now, use symbo 0 or 1. For example, to change the SDS color to red, issue the command:

ArcEdit: sds 0 red

p. 5.33: EditDistance

To change the searching tolerance for selecting features, use the EditDistance command. You can set the ED interectively on screen or with the digitizer, or you can set it with a number (specified in coverage units).

p. 5.33-34: OOPS - be careful

You can undo recent changes with the OOPS command, however, there is no REDO command. For example, if you have added 20 arcs with the ADD command. One of those arcs is in the worng place. You issue the OOPS command, and all 20 arcs disappear, even though you only want to remove the last one added. You will have to re-add all 19 arcs.

p. 5.35: MOVE nodes?

When you edit nodes, you will notice that you may not be able to SELect nodes the same way you SELect arcs or labels. If node topology has not been built and you want to MOVE a node, you will have to issue the MOVE command first, and then you will be promted to select a node for movement. If node topology has been built, you will be able to SELect nodes first and then issue the MOVE command.

You cannot DELETE nodes directly. Nodes only exist in relationship to arcs. To remove a node, you have to remove the arc that it is part of.

p. 5.37: Correcting errors: mouse or digitizer?

Common sense should dictate when to correct errors with the mouse and monitor instead of the digitizer. The textbook suggests always using the digitizer to add data, but in the case of a missing label, it is much faster and easier to simply add the label using the mouse. This is especially true if you only have to add a few labels, and your map is not registered to the table. In the case of a large missing arc, however, you will have to use the digitizer.

p. 5.39: Missing tics

Do not worry about the missing tics. Just use the ones that you have on the manuscript.

p. 5.48: Remove dangling arc

If the dangle shown on this page was not split at the intersecting arc, you would have to split it before removing it. There are several ways you can do this:

Arcedit: sel; split

Arcedit: int all; sel; move parallel 0; int off

p. 5.49: EXTEND sometimes fails

Sometimes EXTEND fails to extend an arc. In this case, follow the procdure:

1. SELect the arc to which the undershoot will be extended
2. SPLIT this arc at the point at which you want to make an intersection (create a pseudo-node).
3. EF node; select the undershoot dangle node.
4. set NODESNap to a distance appropriate for snapping these 2 node
5. MOVE the dangle to the pseudo-node.

p. 5.55: BUILD sometimes fails

If your edits have inadvertently created more errors (i.e., intersection errors), you may not be able to perform a BUILD. In this case, use the INTERSECTERR command to locate and correct these errors before BUILDing again.