Decision-making for how to choose specific visuals or media for expressing meaning is a challenge. To answer with my perspective, Paul, it's one part audience, one part concept. Meaning is somewhere in between the audience (who have varying backgrounds and will interpret concepts differently) and the concept itself.
This type of decision-making is a challenge for a lot of folks -- it's a challenge for me and I've been doing it for almost 20 years:) Fortunately, there are some really great models and toolkits that can help to scaffold the decision-making process. These are all tuned for drawing your own visuals but the same concepts apply to picking and assembling pre-made assets or building technical illustrations:
- Dan Roam offers some free tidbits on his napkinacademy.com site. Pretty nice assortment of tools for subscribers and some practice and feedback support if you'd like to pay a little bit to interact with the author. Good value.
- Dave Gray offers some great ways to think about *what* and *when* to draw.
http://www.davegrayinfo.com/2012/12/17/how-to-know-what-to-draw/- Sunni Brown has a ton of great stuff on her site at
http://sunnibrown.com/doodlerevolution/. She recently released a book with the same title.
- Mike Rhode published a beautiful book last year called the Sketchnote Handbook (http://rohdesign.com/sketchnotes/). He offers plenty of tips for getting started, making choices, and assembling a sketch into a cogent whole.
- The Art of Explanation (http://artofexplanation.com/) from the folks at CommonCraft dispenses LOTS of fantastic advice that could help with these choices.
- A fellow named Danny Langdon (http://www.perforanceinternational.com) put together a framework and set of job aids for information visualization back in the 70's and 80's. I haven't been able to find it in print but I have a copy of a bunch of his stuff. If you can find his decision grids for procedures, processes, classifications, structures, facts, and concepts - hold onto them:) Good stuff.