Creating and editing multipart polygons

Multipart features are composed of more than one physical part that only references one set of attributes. For example, the individual islands that make up Hawaii are often represented as a multipart polygon feature. You can create, edit, and work with multipart features using editing tools as well as geoprocessing tools.

Here are some of the common tasks performed when working with multipart features:

• To create a new multipart feature, create a sketch of the first part, right-click, then click Finish Part. Draw the sketch of the next part, and finish the sketch when you are done creating all the parts. (A shortcut to the Finish Part command is to hold down the SHIFT key and click.)
• To create multipart features from existing polygons by aggregating them based on attributes, you can use the Editor > Merge command (produces multipart polygons when the selected polygons are not contiguous) or the Dissolve geoprocessing tool, and specify that the output have multipart polygons.
• To add a part to an existing feature, create a new feature in the same layer, select it, then use the Editor > Merge command.
• To remove a part from an existing multipart feature, double-click the feature with the Edit tool, right-click the part you want to delete, point to Part, then click Delete. Finish the sketch when you are done.
• To separate parts into individual polygon features, you can select them and use the Explode command on the Advanced Editing toolbar. You can also run the Multipart to Singlepart geoprocessing tool.

Keep in mind that parts in a multipart polygon are spatially separated. They can touch each other at vertices, but they cannot share edges or overlap. When you are sketching a multipart polygon, any parts that share an edge will be merged into a single part when you finish the sketch. In addition, any overlap among parts will be removed, leaving a hole in the polygon.