GIS Lab Exercise #4 - Cleaning Up a Coverage in Arc and ArcEdit

by Thad Tilton Department of Geography and Earth Resources Utah State University Logan, UT 84322-5240 ttilton@geog.usu.edu

Once you have digitized a coverage into Arc/Info, it is necessary to edit your coverage in order to clean up minor errors. The most common types of errors are arc overshoots and undershoots. The commands listed below are ones you will most often need to clean up a coverage. Follow through the commands listed at the bottom of this page to edit the ownership cover you digitized last week.

Arc Commands:

CLEAN <in_cover> {out_cover} {dangle_length} {fuzzy_tolerance} {POLY | LINE}

The clean command will snap together arcs that are within a certain distance (fuzzy tolerance) and remove arcs that are smaller than the dangle length. It will also put a node at each arc intersection. Polygon or arc topology will be built.

BUILD <cover> {POLY | LINE | POINT | NODE | ANNO.}

Use build to create topology. There is no need to use build if you have already used clean. Use build with the point option for point coverages (never use clean for points!).

CREATELABELS <cover> {id_base}

The createlabels command will add labels for each polygon in the coverage, and remove labels that are no longer associated with a polygon. Use clean or build first to insure that polygon topology exists.

ArcEdit Commands:

EDIT <cover> {feature_class}

Specifies which coverage will be active for editing.

EDITFEATURE <NONE | ARC | NODE | LABEL | TIC | LINK | POLYGON ...etc>

Specifies which features of the editcoverage will be active for editing (arcs, lines, points, etc ).

NODESNAP <FIRST | CLOSEST | OFF > {DEFAULT | * | distance}

Snaps nodes together within the specified distance. With the * option, you can define a distance on the screen with the mouse.

SELECT {ONE | MANY | ALL | OUTLINE | DANGLE | CONNECT | UNCLOSED}

SELECT <BOX | POLYGON | CIRCLE | SCREEN > {WITHIN | PASSTHRU}

SELECT {FOR} {LOGICAL EXPRESSION}

After the editcover and the editfeature is specified, select can be used to choose specific features to be edited or removed. Use the mouse and the numbers on the keyboard to select.

DELETE

Use the delete command to remove selected items.

DRAWENVIRONMENT

                           ALL {ON | OFF}
                           ARC {ON | OFF | IDS | ARROWS | INTERSECT}
                           NODE {ON | OFF | IDS | ERRORS | DANGLE | PSEUDO}
                           LABEL {ON | OFF | IDS}
                           TIC {ON | OFF | IDS}
                           ANNO{.subclass} {ON | OFF | level...level}
                           LINK {ON | OFF}
                           POLYGON {ON | OFF | IDS | FILL}
                           REGION.subclass {ON | OFF | IDS | FILL}
                           SECTION.subclass {ON | OFF | IDS | ARROWS | MEASURES | POSITIONS}
                           ROUTE.subclass {ON | OFF | IDS | ARROWS | ROUTEERRORS | MEASUREERRORS}
                          GROUP.subclass {ON | OFF}
Sets the features to be drawn once the draw command is given. Give the drawenvironment as NODE DANGLE to draw boxes around nodes that are not snapped.

SNAPCOVERAGE <cover>

Specifies which coverage will be active for editing with the snap command.

SNAPFEATURES <NONE | ARC | NODE | LABEL | TIC , etc.> <NONE | ARC | NODE | LABEL | TIC , etc>

Specifies which feature will be snapped to which feature when the snap command is given . Requires TWO parameters (NODE ARC, NODE NODE, etc.).

DISTANCE

Use the distance command to find the distance between any two features in the coverage. Once the distance command is given, use the mouse and the numbers on the keyboard to define a distance.

SNAPPING <OFF | FIRST | CLOSEST > {* | DEFAULT | distance}

Specifies how features will be snapped and within what distance. If the distance is known (by using the distance command, e.g.), it can be specified. Otherwise use the * option to define a distance.

SNAP

Snaps only those items that have been selected (using the select command), in the specified coverage (snapcoverage) within the distance given (snapping closest {distance}).

SPLIT

Splits the selected arc at the point specified. This command is useful when you want to delete only part of an arc. First select the arc, then Arcedit will ask you where you want the arc to be split (with the mouse).

EXTEND {* | DISTANCE}

Extends the selected arc in a straight line to the nearest arc within the specified distance. Use the * option to define a distance on the display with the mouse. If no arc exists directly in front of the selected arc within the given distance, the arc will not be extended.

OOPS

Undoes the last edit that was made (accidental deletion, e.g.). Issuing the OOPS command 4 times will undo the last 4 commands, eg.
(Do you think this command may be handy???)

Follow through the commands below (in RED) to edit your coverage.....

Begin at the Unix prompt in the proper directory (containing cache_own)....

major{ttilton): arc

Arc: clean cache_own cache_owncn

Arc: createlabels cache_owncn

Arc: arcedit

Arcedit: display 9999

Arcedit: editcoverage cache_owncn

Arcedit: mapextent cache_owncn

Arcedit: editfeature arc

Arcedit: de arc label tic

Arcedit: de node dangle

Arcedit: nodecolor dangle 2

Arcedit: nodecolor node 3

Arcedit: draw

Arcedit: snapcoverage cache_owncn

Arcedit: snapfeatures node arc

Arcedit: snapping closest .05

At this point you can use the 'select', 'snap', 'extend', 'delete', and 'add' commands to clean up your coverage. Get rid of overshoots with 'delete', and fix undershoots with 'snap'. Make sure to check those polygons that do not have labels and nodes that have been displayed with a red box around them (dangles). Use your Pan/Zoom tool (at the top of the display window) to move in close to the features you are editing. After editing your coverage, leave Arcedit by typing quit (or q) and then answering Y to save your changes.

Assignment

Follow the instructions below. You should first make sure you are in Arc and in the proper workspace (the one that contains your ownership cover). Remember the commands W and LC to move between workspaces and list coverages in your workspace?

Arc: clean cache_owncn
Arc: labelerrors cache_owncn

1) What is the difference between the clean command performed here and the one you did previously?
Which one do you think is better to use in most cases? Why?
2) What does the labelerrors command do? How many polygons have label errors in cache_owncn?

Continue ...
Arc: createlabels cache_owncn
Arc: labelerrors cache_owncn

3) How many label errors do you now have for cache_owncn?

Typing commands < text_string > , in addition to listing all commands that begin with text_string, will also tell you the abbreviation for those commands. For instance, typing commands arce at the Arc prompt will return ArcEdit . since this is the only Arc command beginning with the string arce. Because only the A and the E are capitalized, you can abbreviate the command arcedit with the command ae.

4) Find the abbreviations for the following commands (remember: some of these commands are Arc commands while others are Arcedit commands, make sure you are typing commands at the proper prompt).

drawenvironment
snapfeatures
arcplot
transfersymbol

To recieve credit for lab exercise #4, please e-mail answers to the questions above to: gisclass@geog.usu.edu