Don't worry your not the only one who doesn't know much about this topic. It really is esoteric, and after 3 years of comprehending similar things this is my first attempt at it. I usually just do flow mapping.
your interpretation was real close. There is no direction, it can go either way. Hence no arrowheads or the like. The left side just show how much degradation I found in my analysis (30,719 meters of trails were in a degraded state), which has be divided into my 5 study region where I conducted my analysis (6000m in A; 12,000m in B, etc...). The right side show how much of 30,719 m of degraded trail occurred in each hillslope unit. The middle is just like you said, the contribution.
Once you can read them than you should be able to look quickly and tell that I found very little degradation in Study region A on Hillslope Unit 5, however, a majority of my Hillslope Unit 5 degradation came from Study Region E.
The argument is that you can't quickly gather that information from rows and rows, and columns and columns of numbers. As you can tell, I believe in that.
Thanks for the comments,
"Ah, to see the world with the eyes of the gods is geography--to know cities and tribes, mountains and rivers, earth and sea, this is our gift."