To add a diagram, open the vector's Layer Properties window and then click on the Diagrams tab. The Diagrams tab, as shown in the following screenshot, has five sections, as well as a Diagram type selector.
QGIS supports the addition of three diagram types as overlays on top of vector data. The three diagram types are pie chart, text diagram, and histogram. The underlying vector data can still be styled to provide a nice base map.
The Diagram type selector allows you choose which type of diagram to use: Pie chart, Text diagram, or Histogram. When you choose a type of diagram, the other five sections change to contain the options that are appropriate for the diagram type.
The sections are Attributes, Rendering, Size, Placement, Options, and Legend. Attributes is common to all diagram types and provides the mechanism...