Topology in GIS Wikipedia

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Using ArcGIS to check topology
Using ArcGIS to repair topology
Set up the editing environment
Repair Gap Errors (limited to one polygon at a time)

This image shows an administrative unit polygon file, where a new topology was created to produce the layer shown in red outline. The map shows the extra lines in red inside the external boundary (in this case the international boundary), these represent the topological errors.

Using ArcGIS to check topology

Create Empty Geodatabase

In ArcCatalog, go to the folder where you want to save the geodatabase.
Right click in open space and choose New > Personal Geodatabase
Name the geodatabase ISO3_update_yymmdd.mdb (e.g. usa_update_070801.mdb)

Create Feature Dataset

Right click on the geodatabase and choose New > Feature Dataset
Name the dataset ISO_topology (e.g. usa_topology). Click Next.
Select the Geographic Coordinate System > World > WGS 1984. Click Next
For the vertical coordinate systems, leave as <None>. Click Next. Click Finish

Import Layer to Feature Dataset

Right click on the feature dataset and choose Import > Feature class (single)
Specify the following:

Input Features: The path to the data under check
Output Location: The empty feature dataset created in section 2 above
Output Feature Class: Name the feature class ISO3_work_yymmdd

Create Topology

Right click on the feature dataset (ISO3_topology) and choose New > Topology
Click Next.
Accept the default name (ISO3_topology_Topology) by clicking Next
Select the feature that will participate in the topology and Click Next
Click Next
Click Add Rule
Select Rule > Must Not Overlap and Click OK
Leave Show Errors checked
Click Add Rule
Select Rule > Must Not Have Gaps and Click OK
Leave Show Errors checked
Click Next
Click Finish
Click Yes to validate the topology

Visualize Errors of the Topology

Click on ISO3_topology_Topology and the Preview tab
If the preview of ISO3_topology_Topology shows only one red line that follows the outline of the main polygon, the file is free of topological errors.
If the file has topological errors, it will have multiple lines; one associated with the main polygon, and the others associated with the locations of the gaps and/or overlaps in the data (see Figure 4).

TIP:If the dataset has very poor topology, feature coordinates may collapse when you validate the topology, even with a low cluster tolerance.To prevent this, go to Data Management Tools > Features > Repair Geometry and repair the geometryBEFOREcreating the topology.

Using ArcGIS to repair topology

One of the most common problems in data quality is the presence of gaps or overlaps in polygons such as administrative boundaries. Detailed technical guidance for editing data topology in ArcGIS is below.

Set up the editing environment

Open ArcMap

Import into ArcMap ISO3_topology_Topology (created in Quality Check on page 11)
Click on Yes to add feature classes that participate in topology

Set the Editing Parameters In order to perform the editing procedures, it is important to set the editing parameters as follows:

Change map Units

Go to View > Data Frame Properties
Click on the General Tab
Change Units Display: to Meters
Click Apply > Okay

Set up the parameters

If its not already there, add the Editor toolbar to your workspace by going to View > Toolbars > Editor
On the toolbar, go to Editor > Options
Under the General Tab chose Snapping Tolerance: 50 map units
Under the General Tab choose Sticky Move Tolerance: 1000 map pixels (This will prevent accidental moves of polygons during the editing process.)
Click OK

Start the Editing Process

Start Editing

Click on Editor > Start Editing
Select the Task: Modify Feature and the Target: ISO3_work_yymmdd

Set Snapping Parameter

Go to Editor > Snapping
For the ISO3_work_yymmdd layer, check the boxes for Vertex and Edge
If toolbar not already opened, add Topology Tools
Go to Editor > More Editing Tools > Topology (another toolbar will be added)

Shows ISO3_topology_topology in red and ISO3_work_yymmdd in blue

Repair Overlap Errors

Select Map Topology from toolbar > Select ISO3_work_yymmdd > Click OK
Go to Topology toolbar > Click on <Map Layers> and Select ISO3_topology_Topology
Select all Overlap Errors using the Error Inspector tool > Show ISO3_work_yymmdd Must Not Overlap > Click on Search Now
Select all the errors
Correct the selected Overlap Errors using the Fix Topology Error tool > Right click on the map and choose Subtract
Verify there is no more error with the Error Inspector tool (by repeating the Search Now command as above)
Go to Editor > Save Edits

Repair Gap Errors (limited to one polygon at a time)

Zoom to error
Using the Fix Topology Error tool (), select all the topological errors associated with one of the polygons > Right Click > Select Create Feature (see Figure 7)
Figure 7 - Shows the topological errors selected from ISO3_topology_topology in black
Select the polygon and the new polygons created using the Edit Tool () or open the attribute table and highlight the main polygon and the newly created polygons (they will be at the bottom of the table and have null values).
Go to Editor > Merge to merge the selected polygons. Select the main polygon as the feature with which polygon will be merged (to keep the Attributed Table information) > Click OK.
Save Edits
Continue for all errors