[AmE - not a teacher]
I believe you are referring to the graphic at the right side, here? (The URL doesn't seem article-specific, and therefore may be transitory.)
The "county leaders" graphic is denoting which candidate is leading which state county. You are expected to know the counties on sight (I don't!).
The "size of lead" graphic is denoting how large the support is for each candidate. Notice that each candidate is assigned a color.
Student or Learner