What was persuasive and ahead of its time about the “ghost map” that John Snow created? What are some ways that it anticipated the maps (Google maps, for example) that many rely on today?

What does Johnson mean when he states that Snow’s and Whitehead’s friendship and collaboration was a “triumph of urbanism” (203)?

Johnson states approvingly of Snow and Whitehead that they were both “amateurs” in the work that they did together on cholera transmission. What do you think that he means by this, and how do you think that amateurism, in this context, might be a positive quality? How might it be preferable, in some ways, to being an expert?