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How To: Cut a multi-part polygon and merge the individual parts to create a new multi-part polygon within the same layer

Summary

When splitting part of a multi-part polygon, one part remains with the original (unsplit) feature, while the other part becomes a new feature. The part that remains with the original feature as a multi-part polygon is merged. However, it may be necessary to unmerge and switch the parts of the polygon. Consider the island of Borneo to represent a multi-part polygon, with each part belonging to a different country. The portion of Malaysia on Borneo must be associated with the portion of the Malay peninsula, but the Cut Polygons tool may associate the Indonesian (or Bruneian) part of Borneo instead. In the image below, this error must be rectified.

In the image provided, Indonesian Borneo is incorrectly associated with the Malay peninsula in the multi-part polygon.

This article describes how to unmerge the multi-part polygons and select another polygon to be associated with the original feature within the layer.

Procedure

  1. In ArcMap, start an edit session. Click the Editor menu and select Start Editing.
  2. On the Editor toolbar, click the Edit tool The Edit tool. , and select the multipart polygons.

    An image of the multipart polygons and the attribute.
     
  3. Click the Cut Polygons tool The Cut Polygons tool. on the Editor toolbar.
  4. Drag the Cut Polygons tool across the polygon, and double-click the end of the segment to finish the cut operation. Note that one of the cut polygons is still merged as a multipart polygon with the original (unsplit) polygon, while the other part becomes a new feature.

    An image showing one part of the cut polygon multipart with the original feature, while the other part has become its own feature.
     
  5. On the Advanced Editing toolbar, click the Explode Multipart Feature command An image of the Explode Multipart Feature command. to split the multipart polygons into individual features. Note that all the features are no longer a multipart feature.
    Note:
    The Explode Multipart Feature command requires the Advanced Editing toolbar.
    

    An image of the split features and the attributes.
     
  6. Click the Edit tool, hold down the Shift key, and select the original (unsplit) feature and the desired feature to be merged.
  7. Click the Editor drop-down arrow, and click Merge to create multipart features.

    An image of merging the original feature with the selected cut polygon.
     
  8. Click OK on the Merge dialog box. Note that the original feature is now a multipart polygon with the selected feature.

    An image of the original feature merged with a selected feature to become a multipart polygon.
     
  9. Click Save Edits from the Editor drop-down arrow.

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