Then maybe you could make them proper pie charts with the city symbol in the middle? The various 'thicknesses' (is that even a word?) seem kind of confusing to me if they do not bear any additional information...
For the spead of the plage, maybe think of isolines or however they are called in english? So one city as the starting point, and then some lines for "the plague has spread this far after 3/6/12/.../n months? (You know, like height lines on topographic maps.)
But I don't think it is a good idea to add a "infected" number in the ring, I'd keep it just 'survivors' (the blank part) and 'deceased', if you want to show what the plague did everywhere in retrovision. If you want to make it a snapshot of the ongoing pandemic, however...
And another thought about the rivers: Maybe make them a bit wider? I find them kind of hard to see at a glance, but in a medieval fantasy world they've got to be important travel routes, I suppose.
