Dissolving Features & Summarizing Attributes (with the Aggregate Tool)
QGIS’s Aggregate tool performs a “dissolve” operation while calculating summary statistics on attribute values. This tutorial reviews the Aggregate tool and demonstrates with an example.
Included in this tutorial:
Accessing the Aggregate tool
The Aggregate Tool Parameters
Running the Tool and Examining the Results, with an example
Software version in examples: QGIS 3.84 Prizren
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: L. Meisterlin (2026)
Related Tutorials:
Accessing the Aggregate Tool
To access the Aggregate tool in QGIS, you can navigate through or search the Processing toolbox.
finding the Aggregate tool by searching the Processing toolbox
finding the Aggregate tool within the Processing toolbox
The Aggregate Tool Parameters
The aggregate parameters are straightforward. From top to bottom, they are…
Input layer: Select the vector layer with features you want to aggregate. Note the checkbox option to operate upon the selected features only if your input layer has an active selection.
Group by expression: Here, you have three approaches to grouping your features when aggregating.
Choose from the dropdown list of the input layer’s attribute fields to dissolve or aggregate based on a shared attribute value
Use the Expression Builder to the right of the dropdown to group features based on a specific expression.
Leave the option blank (or null) to aggregate all features in the layer.
Aggregates: By default the Aggregates list includes all attributes in the input layer with default options for how to summarize feature values.
Add or remove attributes from the list (or reorder them within the output’s attribute table) by using the buttons to the right of the list, highlighted in the image below.
Change the Aggregate Function to specify the calculated summary.
Change the Name of the output field containing the summary.
Change the output field’s data type in the Type column option.
Output options are typical for QGIS: You can create a temporary layer or specify where to save the results and what to name the layer. You can also choose whether to add the output file to the current map project.
the Aggregate tool dialogue box with example inputs
Running the Tool and Examining Results, with an example
In this example, we will aggregate contiguous polygon features (representing census tracts) based on their shared value in the attribute field called Categ. In the process, we calculate the sum of values in the Int_sm field. The tool’s parameters are illustrated in the image above, and the input layer is illustrated in the image below.
the example input layer
We expect that the output layer will include fewer, larger polygons with boundaries matching the color-coded features in the symbolized map above. We also expect that the output attribute table will include one summary field.
After running the tool, we see that our results are as expected. We have multipart features that correspond to the Categ field values used to group the input features, each with a calculated sum of the input layer’s Int_sm attributes.
the example’s results with newly aggregated polygons symbolized by the Int_sm values