Dissolving Features
To aggregate or combine vector features based on shared attribute values is to “dissolve” them. This tutorial reviews the Dissolve tool in QGIS and demonstrates with an example.
Included in this tutorial:
Accessing the Dissolve Tool
The Dissolve Tool Parameters
Running the Tool and Examining the Results, with an example
Software version in examples: QGIS 3.84 Prinzen
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: L. Meisterlin (2025)
Accessing the Dissolve Tool
To access the Dissolve tool in QGIS, you can click through Vector > Geoprocessing Tools > Dissolve in the main menu. Alternatively, you can find the same tool by navigating through or searching the Processing toolbox.
the Dissolve tool in the Main Menu
the Dissolve tool within the Vector geometry tools in the Processing Toolbox
Notice that multiple vector geoprocessing toolsets within QGIS contain a tool to accomplish a dissolve operation. This tutorial will walk through and demonstrate the QGIS Vector geometry tool (the one that is highlighted in the image above).
The Dissolve Tool Parameters
The dissolve parameters are relatively straightforward (and minimal in number). They are…
Input layer: The vector layer containing the features to be aggregated or combined, including a checkbox option to operate upon the selected features only (if your input layer contains an active selection).
Dissolve field(s): This optional parameter allows you to select one or more fields from the input layer’s attribute table to serve as the basis of the dissolve operation.
To access a list of fields, click the ellipsis [...] button to the right of the parameter. Features sharing the same value within the “dissolve field” will be aggregated together into a single feature.
Leaving this parameter blank will aggregate (“dissolve”) all features of the input layer into a single feature in the output.
There is an additional optional (“advanced parameter”) checkbox option to keep disjoint features separate. By default, this option is unchecked: nonadjacent features containing the same value in the dissolve field(s) will be aggregated into multi-part features. Checking this box will separate nonadjacent features into distinct features in the output, regardless of whether they share a value in the dissolve field.
The Output Options are the same as other vector geoprocessing tools in QGIS. At the bottom of the dialogue box (under Dissolved), you can choose whether and where to save the output or create a temporary layer. You can also choose whether to add the output ot the current map using the checkbox option.
The Dissolve tool parameters, with example inputs
Running the Tool and Examining the Results, with an example
In this example, we will dissolve contiguous polygon features (representing census blocks) based on their shared values in the “CT2010” field of the layer’s attribute table. This field represents census tracts, and we know that each census tract comprises multiple census blocks. Thus, we expect fewer and larger aggregated polygons in the result.
the example inputs, with the “dissolve field” highlighted in the attribute table
Note that the input layer contains 1,296 polygon features.
After running the tool (the specific parameter options are illustrated in “The Dissolve Tool Parameters” section above), we see that our results are as expected: fewer, larger polygons, wherein each is the aggregation of the blocks that share a value in the “CT2010” (census tract) field. Note that the output layer (called “Dissolved” in the image below) contains only 89 polygon features.
the example’s results with newly created dissolved polygons symbolized as pink-outlined polygons