As the examples will make clear, the figures use warmer colors – orange and red – to show counties for which the factor being considered has a higher value or change. Lower values or changes are indicated by cooler colors – shades of green – and yellows indicate areas where the factor under consideration has a moderate value or change.
  What don’t we know?   Finally, how should that knowledge, and the limits to it, guide our response to the boom? What do we know about previous booms? I am going to re-use a chart that originated in a research paper by Jonathan Kearns and Christian Gillitzer 1 , with some updating.