Each bubble is a School District total of the percentage of students either Overweight or Obese in New York State school systems, since 2010. Dataset here.
This is an example of the d3 Pack layout with a linear, sequential color scale. Bubbles get bigger and become more red as their percentage of overweight/obese students increases.
Modified http://d3js.org/d3.v3.js to a secure url
https://d3js.org/d3.v3.js