By David Crowther
Question:
How do you extract Centroids from Polygons within QGIS?
Answer:
The Centroids Tool within QGIS enables you to create a Points Layer based on the Centroids of your input Polygon Layer.
In QGIS below I have a Polygon Layer showing the Ward boundaries for the London Borough of Islington.
We are going to create a Points Layer based on the Centroid of each Ward Polygon.
From the Processing menu choose > Toolbox > and open the Vector Geometry section.
Choose the Centroids menu option.
The Centroids Tool will open.
In the Input Layer choose your Polygon Layer > LBI Wards. Then in the Centroids option, you could choose to save the result as a GIS file, or leave as it is and create a Temporary Layer.
If you now Run the Centroids Tool, the result will be a new Temporary Layer called Centroids.
In your Layers Panel you will now see the new Temporary Layer called Centroids and in the map, you now have Point objects at the Centroid of each Polygon in your input layer.
You can now use the Points Layer to generate Graduated/Proportional Circle Thematics from the centre of each Polygon, thus allowing you to visualise two different Thematics for the same data!