2 ways to create a multipart polygon
Problem: You need to create a second distinct polygon that is attached to the same record in the attribute table.
A multipart polygon is a group of polygons that have gaps between them, but only one attribute table entry (and therefore only one object ID). They might be used in a case where there are multiple buildings on the same parcel, multiple zones of influence for the same actor, or multiple lilypads on the same pond. If all the attributes are the same, might as well use the same record for all, instead of a long list of repeating values. You will know you are dealing with multipart features if you click on one polygon to select or identify it, and other polygons light up too. But how do you create one?
I know of two ways: one I have been doing for a long time and another I just learned. I will start with the new way, although I think I still prefer the old. Both sets of instructions assume you have already digitized the first polygon.
Tacking on a multipart, Way #1:
- With the editor tool (black arrow), select your polygon.
- Change the edit Task to Modify Feature.
- Switch to the sketch tool (yellow pencil). Lines will extend out between your starting and ending vertices.
- Hover over one of these vertices and right click to Finish Part.
- Digitize your next polygon like normal. When you have created the final vertex, right click to Finish Sketch.
Or, select Finish Part if you want to create additional polygons in the multipart feature. Finish Sketch when you’re done creating the last one.
You have to follow these steps exactly as I have written them or it won’t work. I find this procedure a little nit-picky but it may just be because I am not used to it yet. The only advantage I can think of is that you never end up of creating a second attribute record this way, which may help in keeping object IDs straight.
Tacking on a multipart, Way #2:
- Digitize your second polygon in the normal way.
- With the Edit tool, hold down the Shift Key to select both polygons.
(Or, click and drag to draw a box around them) - Select Merge from the Editor menu.
Try them both and pick your favorite!
October 21st, 2009 at 3:15 pm
Better to plan multiparts when editing the first feature: do not end that feature with a doubleclick or F2, but choose from the context menu Finish part. You are able to directly continue with the second part.