However, there are a number of larger population centers, which means more drivers and more accidents which tends to drive the rates back up. (thesimpledollar.com)
You are seeing population centers of various sizes, which we will call nodes. (realclimate.org)
It is even not shameful that we tried originally to put the power plants that use this fuel away from population centers so as to minimize damage from the truly dirty emissions. (realclimate.org)