Posted on December 27, 2022 (Updated on July 21, 2025)

PyQGIS – Creating Pie Chart

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PyQGIS: Slicing Up Spatial Data with Pie Charts – A Visual Feast!

Let’s face it, geospatial data can be a beast. It’s often complex, sprawling, and just plain overwhelming. That’s why we need clever ways to visualize it, to tease out the stories hidden within those layers and attributes. QGIS, being the awesome open-source GIS powerhouse it is, gives us plenty of tools for this. And when you combine it with PyQGIS, its Python API, well, the possibilities explode! One of my favorite tricks? Pie charts. They’re a fantastic way to show the composition of categorical data right on the map, turning abstract numbers into something instantly understandable. So, let’s dive in and see how we can whip up some pie charts using PyQGIS.

The Lay of the Land

Before we start slinging code, let’s get the basics down. In QGIS-speak, pie charts are a type of “diagram renderer.” Think of it like this: for every feature in your vector layer (that polygon representing a neighborhood, for example), QGIS will draw a pie chart. The size of the whole pie, and the slices within it, reflect the values of the attributes you choose. Simple, right?

Key Ingredients for Your PyQGIS Pie

To bake these pies, you’ll need a few key ingredients from the PyQGIS library:

  • QgsVectorLayer: This is your data, the vector layer holding all those juicy features you want to visualize.
  • QgsPieDiagram: This tells QGIS, “Hey, I want a pie chart!”
  • QgsDiagramSettings: This is where you get to customize your pie. What attributes determine the slice sizes? What colors should they be? Do you want labels? This is where you set it all.
  • QgsLinearlyInterpolatedDiagramRenderer: This is the artist, the one who actually draws the pies on your map. It can even scale the pies based on another attribute, making them bigger or smaller depending on the value.

Let’s Get Cooking: Step-by-Step

Okay, time to get our hands dirty! Here’s a step-by-step recipe for creating pie charts with PyQGIS:

  • Import the Goodies: First, bring in those PyQGIS classes we talked about. Think of it as gathering your ingredients.

  • Load Up Your Layer: Next, load the vector layer you want to work with. This could be a shapefile, a GeoJSON, whatever floats your boat.

  • Declare Pie Time: Create a QgsPieDiagram object. This is like saying, “Alright, we’re making pies!”

  • Configure Your Pie: Now, the fun part! Create a QgsDiagramSettings object and tell it which attributes to use for the slices. Pick your colors, add labels – make it pretty!

  • Hire an Artist: Create a QgsLinearlyInterpolatedDiagramRenderer object. This renderer takes your settings and draws the pies on the map. You can tell it to scale the pies based on an attribute, too.

  • Assign the Artist to the Layer: Tell your vector layer to use this fancy new renderer. This is like saying, “Hey QGIS, use this pie chart thingy when you draw this layer!”

  • Refresh and Admire: Finally, refresh the map canvas to see your beautiful pie charts in all their glory.

    • Code Snippet: A Taste of PyQGIS

    Here’s a little code to get you started. Copy, paste, tweak, and enjoy!

    python

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