Junji Zhi has an interesting post on drawing diagrams in Emacs. He wanted to draw diagrams for system modeling and do it from within Emacs. There are several ways of accomplishing that but Zhi chose Mermaid. It basically provides a markup language for the diagram and then renders a PNG. It’s much like the Graphviz’s dot language that I usually use for this type of thing.
For those who prefer a more visual approach, there’s ditaa, which takes an ASCII art diagram and turns it into a very nice looking PNG picture. It’s really easy to use but I rarely turn to it because I find Emacs’ Artist Mode difficult to use. That’s probably because my manual dexterity is challenged even to the extent of dealing with—for most people—the excellent artist-mode.
The point is, there is almost certainly a way of drawing a diagram in Emacs that you will find comfortable. I’ve never used Mermaid but it seems like a nice program that’s pretty easy to use. I’ll probably keep using dot because I’m used to it and it’s similar to Mermaid. I’ve used ditaa but mostly just as a test drive. If you’re good with artist-mode, ditaa is a quick and easy way of getting a diagram without having to learn a markup language.
As usual, Emacs lets you have it your way. Whichever way of drawing diagrams is most natural for you, Emacs has a package that supports it.