Editing tools to create multipart polygons, specifically donut polygons.

12-01-2021 12:27 PM
Esri Contributor
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In this blog, I will discuss how to create a multipart polygon, specifically a multipart polygon with holes, also known as a donut polygon. Although this article focuses on polygons, some of the functionality discussed here is not specific to polygons so please try it out with your workflows and let us know what you think. I will describe four interactive methods that result in polygon features with donut holes: Create a new multipart polygon; Create a new polygon with the clip intersecting option to modify an existing polygon; Modify an existing polygon using the Continue Feature tool; Modify an existing polygon and output a new polygon using the Split tool.

Creating new polygon features

First, I will discuss two workflows to create a new multipart polygon using Feature Template construction tools. From the Create Features pane, choose a Polygon feature template. For sketching a new multipart polygon, we can use one of the following construction tools: polygon, autocomplete polygon, right angle, or trace.

Create a new polygon with a donut hole

I have a sketch in progress and am ready to add the donut hole. To proceed, I add a part to the sketch by choosing Finish Part from the context menu. After choosing Finish Part, the sketch will remain in progress and I simply resume digitizing to add another part. For a donut, I digitize within an existing part of the sketch. When done, I finish the sketch to create the multipart feature.

Create a new multipart polygonCreate a new multipart polygon

If you prefer shortcut keys, either hit F4 on the keyboard or hold down the shift key while double clicking to execute the Finish Part menu item. Without the shift key, double clicking will finish the sketch and create the new feature.

The Finish Part command is available on the following tools’ context menu: Feature Template construction tools, Replace Geometry edit tool, Continue Feature edit tool, and Split interactive edit tool. One more note on the context menu, the context menu may look different depending on the feature geometry type being edited and if the right click is on an edge or in open space.

Create a new polygon and clip intersecting, existing polygons

Some Feature Template construction tools support tool options that can be set at time of use on the Active Template pane or stored with the template’s properties. Polygon construction tools have an option to clip intersecting polygons within the same feature layer. The option takes the input sketch on finish and searches for any existing, intersecting features to clip. In addition to the new polygon, overlapping polygons are clipped and may result in a multipart polygon.

Modify existing polygon features

Now, I will discuss modify tools for updating existing polygons. The modify tools are available from the Edit tab tools gallery or from the Modify Features pane.

Modify an existing polygon to have a donut hole

The Continue Feature tool is the suggested tool for modifying an existing polygon feature to be a multipart polygon or to add additional parts to a multipart polygon. Upon opening the tool, if there is a valid selection, which for this tool is one feature, the tool will be active and the feature sketch is shown on the map. If the selection is not valid, the tool will be in active select mode. Without changing to the core select tool, either select a single polygon feature on the map or, if there are two or more features selected, select one feature on the map or reduce the selection set down to one by interacting with the feature identifier in the tree node. To use the tool, I begin clicking in the map to add vertices to the sketch. I can digitize a part within the existing polygon to create a donut or digitize new distinct parts using the Finish Part capability as described above. When the polygon sketch is ready, I finish the sketch and commit the edits. A new feature is created and the original single part polygon is now a multipart polygon.

Split an existing polygon to have a donut hole

The Split tool, Interactive mode, is the suggested tool to split an existing polygon into two or more features. For my scenario, Split is different from Continue Feature because it results in multiple polygon features, one within the other, rather than one polygon feature with a hole. Like Continue Feature, and the majority of the modify features tools, the tool will activate on open if the selection is valid for the tool’s criteria. If it is not valid, simply update the selection on the map or via the treenode without changing the tool. Split can support multiple selected features but for my case, I just need the one polygon selected. Once I have the polygon selected, I start sketching on the map. Rather than sketching a polygon like I’ve shown in the prior workflows, I am sketching a line. To use Split interactive to create a donut, I need to create a closed loop line by snapping the last vertex to the first vertex. Once I have a closed loop line, I can finish the sketch to create one or more polygons within another polygon.

If mid sketch vertex editing is making it challenging to close the line back onto itself, aside from rushing to the beat the timer, there are two options.  The video shows beating the vertex editing timer as well as the two options I describe below.

The first option is to place the last vertex somewhere near the first. Then, take advantage of the mid sketch vertex editing capability by hovering over the vertex to get into vertex editing mode. Once in this mode, move the vertex and snap it onto the first vertex.

The second option is new at 2.9 and may be the preferred of the two options. It is now possible to toggle off mid-sketch vertex editing on the edit toolbar and then snap the last vertex to the first vertex. Sketch vertex editing can be toggled on/off at any time while using any edit tool that sketches on the map.