Problem: Gaps and dangles appear between lines or edges after editing features


Editing features such as snapping a line, splitting a parcel, or clipping a polygon produces gaps (line undershoot) and dangles (line overshoot) when zooming in to a map scale of less than 1:1.


The problem occurs when zooming in to an unrealistic scale of less than 1:1. The software's limit is a scale of 1:1. At this scale, the screen display is equal to the real distance on the earth's surface. Hence, zooming in to a scale of less than 1:1 pushes the resolution tolerance past the maximum threshold, and produces visual artifacts such as gaps (line undershoot) and dangles (line overshoot).

Solution or Workaround

Use one of the following workarounds to edit features and ensure no gaps and dangles are produced:

Choosing the snapping types before snapping lines

In ArcMap, click the Snapping drop-down arrow, and select the Use Snapping command. Click the snapping types to activate the snapping cue. Each snapping type is represented by a visual cue that matches the icons in the Snapping toolbar. The snapping cue on the screen enables snapping between features.

Enable the snap options.
For visual cues while snapping, navigate to Snapping > Options. Check the Snap tips check box, and other desired properties. Snap tips and snapping cue help to visualize the snapping location.

This is the Snap tips field in the Snapping Options dialog box.

The image below shows the snapping cue (at the tip location where the two lines are about to connect) and the snap tip (represents the snapping properties).

This is the snap tip.

Increasing the Snapping Tolerance value

Increasing the Snapping Tolerance value increases the possibility of snapping.

  1. In ArcMap, click the drop-down arrow of the Command button, and select Options. This opens the Snapping Options dialog box.
  2. In the General section, specify the Tolerance value in pixels.
  3. Click OK.

    This is the Tolerance field in the Snapping Options dialog box.

Increasing the Sticky move tolerance value

Sticky move tolerance prevents features from being accidentally moved. Increasing the Sticky move tolerance value increases the minimum number of pixels the pointer must move before moving a selected feature,thus reducing the possibility of accidentally creating gaps and dangles.

  1. In ArcMap, click the Editor drop-down arrow, and click Options.
  2. In the General tab, specify the Sticky move tolerance value in pixels.
  3. Click OK.

    This is the Sticky move tolerance field.
Applying topology rules

Topology rules enable spatial relationships between features in a single feature class or between two feature classes to be defined. For more information on different topology rules, refer to ArcGIS Geodatabase Topology Rules. Topology rules can be used to identify the occurrence of dangles.

  1. In ArcCatalog, right-click the feature dataset, and select New > Topology. This opens the New Topology dialog box.
All feature classes stored within a geodatabase must be transferred into a feature dataset before creating a new topology.
  1. Accept the default settings and continue to click Next until the page to Specify the rules for the topology appears.
  2. Click the Add Rule button. This opens the Add Rule dialog box.

    This is the New Topology dialog box.
  3. Specify Rule as Must Not Have Dangles.

    This is the Add Rule dialog box.
  4. Click OK.
  5. Add more rules by selecting from the Add Rule dialog box.
  6. Click Next until the last page of the dialog box, and click Finish. Any dangle appearing on the layer is displayed in the map view.
  7. Check for errors. If found, perform a quick fix by right-clicking the individual errors.

Measuring the offset distance against the XY Tolerance value

The default XY Tolerance in ArcMap is 0.001 m, which equals approximately 0.003 feet. A gap or dangle with a value of less than 0.003 feet is considered a coincident.

The image below shows the measurement of an offset distance between a shared boundary after a parcel is split. At a zoom map scale of 1:0.05, the difference between the shared boundary is 0.001552 feet, which is less than 0.003 feet. Hence, the line is considered a coincident.

An example of the gap between lines.

Ensuring data layers use the same coordinate system

Ensure the layers for editing use the same coordinate system. Using different coordinate systems for different layers projects the data differently on the map. Additionally, different coordinate systems or the presence of on-the-fly projection in the datasets can produce distance offsets, which may appear in the form of gaps and dangles.

Running the Find Dangles Check Properties tool from the Data Reviewer toolbar
This tool is available with a Data Reviewer license.

Running the Find Dangles check determines the presence of dangles in the dataset. For more information,refer to Finding dangles on line features.

For additional information on removing gaps for feature polygons, refer to Removing slivers or gaps between polygons.

Related Information

Last Published: 10/4/2018

Article ID: 000017053

Software: ArcMap 10.2.2, 10.2.1, 10.2