Finding polygon overlaps and gaps that are slivers

When polygon features share a boundary and a space between the features along the boundary exists, it is considered a gap. For example, a gap might exist between a lake and grassland area. There can also be overlaps between features. For example, there could be a gap due to an overlap between a coastal water area and the foreshore due to an island. In both of these instances, the gap or overlapping area could be considered a sliver polygon.

Sliver polygons between polygon features often result from creating new polygons without using snapping or editing shared boundaries without a topology.

The Polygon Overlap/Gap is Sliver check finds overlaps and gaps that can be considered slivers. You can choose to find both gaps and overlaps, only gaps, or only overlaps. The thinness ratio and polygon area can be used to define how large or small the gap or overlapping area can be in order for it to be considered a sliver. The check can be run on an entire feature class, a subtype, or a set of features selected using a SQL query.

Once you have defined the criteria for the check, you can configure the notes and a severity rating. The notes allow you to provide a more specific description for the feature that has been written to the Reviewer table and are copied to the Notes field in the Reviewer table. The severity rating allows you to indicate how important the results from a check are in terms of your quality assurance/quality control processes. The lower the number, the greater the priority the check's results have.

  1. Start ArcMap.
  2. On the main menu, click Customize > Toolbars > Data Reviewer.
  3. Click the Select Data Check drop-down arrow on the Data Reviewer toolbar, click the plus sign (+) next to Feature on Feature Checks, then click Polygon Overlap/Gap is Sliver Check.

    The Polygon Overlap/Gap is Sliver Check Properties dialog box appears.

    Polygon Overlap/Gap is Sliver Check Properties dialog box
  4. If necessary, type a unique name for the check in the Check Title text box.

    The check title can be used to describe the conditions you are looking for with the check. This is useful when you have multiple instances of the same check to validate the same feature classes or tables but with different validation parameters.

  5. Click the Feature Class/Subtype drop-down arrow in the Feature Class 1 area and choose the feature class and subtype on which to run the check.
  6. To run the check on the entire feature class and save this setting, check the Always Run on Full Database check box.
  7. To run the check on specific features in a feature class, click SQL to construct a SQL query.
  8. Repeat steps 5–7 in the Feature Class 2 area.

    If you want to run the check using selected features in feature class 1 and all the features in feature class 2, check the Always Run on Full Database check box.

  9. Choose what types of conditions you want to search for slivers.

    You can choose to search for both overlaps and gaps, only overlaps, or only gaps.

  10. Move the Thinness Ratio slider to the position that best describes the thinness of a sliver polygon.

    The farther right the slider is moved, the thicker the polygon must be to be recognized as a sliver.

  11. Type a value for the maximum size of a polygon gap or overlap in the Maximum Polygon Area text box.
  12. Click the SQ drop-down arrow and choose the units of measurement to use with the maximum polygon area.
  13. If necessary, type descriptive text for the check results in the Notes text box in the Reviewer Remarks area.
  14. If necessary, click the Severity drop-down arrow and choose a value that indicates the priority of the check's results in the Reviewer Remarks area.
  15. Click OK.
  16. Click the Run Data Check button Run Data Check on the Data Reviewer toolbar.

    The Features to Validate dialog box appears.

    Features to Validate dialog box
  17. Choose an option in the Features to Validate area.
    • Selection Set—The check is run on the features that are currently selected in the map.
    • Current Extent—The check is run on the current map extent, which is controlled by the map scale.
    • Definition Query—The check is run on the features that are displayed based on definition queries that have been created for the feature class.
    • Full Database—The check is run on all the features in the feature class.
  18. To run the check only on features that have been edited in a versioned workspace, check the Changed Features Only check box.

    The Changed Features Only option is available only for a versioned database.

  19. Click OK.

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