In ArcGIS, how do I create an island polygon?
Sometimes you need to create a polygon with a hole in it, or even a polygon with both a hole and an interior polygon. To create these kinds of polygons, you need to create a multipart feature. When you create a polygon with an island inside it, the outer and inner areas are all one feature. This means that clicking either polygon will select both of them, and the attributes of the feature are stored in just one row in a table. Donut polygons are commonly used with administrative boundaries. For example, a city may have unincorporated areas within its limits.
Cutting donut holes in existing polygons
You can cut holes in existing polygon features to create a donut polygon:
- Open the
Snappingenvironment from the Editor toolbar. Turn on snapping foredit sketch verticesby checking the appropriate box at the bottom of the dialog box. With edit sketch snapping, you can better construct a closed boundary defining the area you want to remove.
- Set the task to
Cut Polygon Features.
- Select the
Sketchtool.
- Sketch the area you want to remove. Make sure the end vertex snaps
to the first one, so you end up with a closed polygon.
- Finish the sketch.
- You now have two polygons. Select only the inner polygon. If you
have trouble selecting only the inner polygon, open the polygon
layer's attribute table and select the polygon there.
- Press the
Deletekey. You can now see there is an island polygon.
To use an existing overlapping polygon for the shape of the hole, use
the Clip command. When using this method, keep in mind that
all editable features underneath the feature you are using to clip
with will be clipped.
- Select the inner polygon.
- Click the
Editormenu, and then selectClip.
- Set the buffer distance to 0, and choose to discard the area that
intersects.
- Click
OK.
- Press the
Deletekey to delete the inner polygon.
For more, see the Online ArcGIS Desktop Help for Common polygon editing tasks.
Last modified on May 13, 2009.
