One chart that I've never seen anyone else (besides myself) develop is the potential number of communication channels per band. If we were so coordinated, we could put one SSB phone channel every 3 kHz. For any region covered by a typical radio, that determines (more-or-less) the number of simultaneous non-interfering conversations. So, assuming that everyone has an Extra-class license (so the maximum spans of frequencies can be used, for simplicity), how many users can the HF ham bands support?

160m: 66; 80m: 133; 40m: 58; 20m: 66; 17m: 19; 15m: 83, 12m: 20, and 10m: 466.

When you compare the number of licensed hams (about 750,000 in the US) against the number of available HF channels, it's amazing that there isn't more congestion! Bear in mind that not all of these bands are effective for communications from point A to point B, depending on the time of day, time of year, and phase of the sunspot cycle. The 10m band has been good only for local comms during the solar minimum, and the 160m band is plagued by industrial noise. In an emergency, if everyone who could, tried to talk at the same time, it would be a Tower of Babble.