Further reading
The smartdiagram package provides a detailed manual with a complete reference to all settings and even its source code. You can open it on your computer at the command line with texdoc smartdiagram or by visiting https://texdoc.org/pkg/smartdiagram.
The LaTeX Cookbook by Packt Publishing and written by me has a Building smart diagrams section in Chapter 9, Creating Graphics. It shows more smartdiagram examples, just not as customized as in this chapter, and with detailed explanations and references. You can find the entire section at https://latex-cookbook.net/9-1-building-smart-diagrams/.
The LaTeX Cookbook explains in detail how to create a complex flowchart from scratch with just standard TikZ tools. This section is also available online; you can read it at https://latex-cookbook.net/9-2-constructing-a-flowchart. You can also find pie charts and Venn diagrams examples in the same book and on its website.
The pgf-pie manual can be found at https://texdoc...
