Problem: A duplicate feature is returned by the dissolve tool of the GeoProcessing wizard
After dissolving layers based on the values of a field, the output sometimes contains duplicate features.
This is due to the following:
- The layer being dissolved includes a record that has no geometry; that is, it has null shape. This could be a result of adding a new record to the layer's attribute table without creating a corresponding shape (point, line, or polygon).
- The record without a shape has a unique value for the attribute being used to dissolve the layer. The dissolve operation creates a new feature in the output based on this unique value. Because this feature is derived from a record with no shape, there should be no shape in the output; instead, the dissolve operation populates this category with duplicate features.
Solution or Workaround
Delete from the output duplicate features created by dissolving a record with no shape. The duplicate features are the ones associated with the value in the dissolved output derived from the record with no shape of the input layer.
- Identify the records with no shape in the original layer.
- Zoom out to the full extent of the map. Use the Full Extent button of the Tools Toolbar.
Note: Make sure all your features are visible.
- Click the Select Features tool of the Tools Toolbar
- Click and drag a box around all the features
- Open the layer's attribute table
- Click Options and select Switch Selection. The highlighted records should be all those records that have null or empty geometry.
- Identify the value of the field used to dissolve the layer. The value for this record with no shape should be unique.
- Click the dissolve output layer and open the attribute table.
- Select the record containing the unique value derived from the record with no shape.
- Click the Editor Toolbar button of the Main Toolbar.
- Click the Editor dropdown menu and select Start Editing.
- Press the Delete key on the keyboard to remove the selected record.
- Click the Editor dropdown menu and select Stop Editing.
- Click Yes to save the edits.