How To: Cut a multi-part polygon and merge the individual parts to create a new multi-part polygon within the same layer
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.
This article describes how to unmerge the multi-part polygons and select another polygon to be associated with the original feature within the layer.
In ArcMap, start an edit session. Click the Editor menu and select Start Editing.
On the Editor toolbar, click the Edit tool , and select the multipart polygons.
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.
On the Advanced Editing toolbar, click the Explode Multipart Feature command to split the multipart polygons into individual features. Note that all the features are no longer a multipart feature.
The Explode Multipart Feature command requires the Advanced Editing toolbar.
Click the Edit tool, hold down the Shift key, and select the original (unsplit) feature and the desired feature to be merged.
Click the Editor drop-down arrow, and click Merge to create multipart features.
Click OK on the Merge dialog box. Note that the original feature is now a multipart polygon with the selected feature.