Considering the image, the idea that is best illustrated by the map is that "the plague started in the south and spread north and west."
This can be seen from the map where the plague started early in the south around December 31, 1347, and later spread towards the north and western part of the map in the subsequent years.
The plague occurred in the West between 1348 to 1349 and later spread to the north around 1349 to 1350.
Hence, in this case, it is concluded that the correct answer is option B. "The plague started in the south and spread north and west."
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