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Combining polygons with Boolean operators
Combining polygons with Boolean operators

Learn how to use the union and intersect tools to analyze your polygon features and layers

Karen Joyce avatar
Written by Karen Joyce
Updated over a week ago

Who can use this feature

Owners and Editors of projects within all Professional and Pro + workspaces

Boolean operators are like magic words that help you make decisions and sort things. For example:

  • AND is like saying, "I want both." If you say, "I want ice cream AND sprinkles," you get both ice cream and sprinkles.

  • OR is like saying, "I want either one." If you say, "I want ice cream OR cake," you get either ice cream OR cake - both if you're lucky!

  • NOT is like saying, "I don't want this." If you say, "I want ice cream, but NOT chocolate," you get ice cream that isn't chocolate.

In geospatial analysis we use Boolean operators to help understand relationships between features on Earth. For example:

  • I want to find areas where there is seagrass AND the area is designated as protected. You'll get the overlapping region. Use the intersect tool to achieve this.

  • I want to find areas where there is seagrass OR the area is designated as protected. You'll get the a much larger region that will contain all areas that have seagrass, all that are protected, and there may be some areas that correspond to the overlap. Use the union tool to achieve this.

Simply, the intersect tool identifies overlapping areas between layers or features, while the union tool combines multiple polygon layers into a single layer.

To perform an intersect or union operation:

  1. Select two or more overlapping features or layers

  2. Click the union or intersect tool from the top menu bar

If you performed the union or intersect on multiple features within the same layer, the new feature will be returned within that layer.

If you performed the union or intersect between multiple layers, a new layer will be created at the top of your table of contents.

The example below consists of three polygon features in a single layer. Each represent the area where field surveys were conducted. But given there is some overlap, we want to know the total area, without duplication. We use the union tool to achieve this.

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