To be accurate, this is the Census Bureau's call, not Arbitron's.
To an extent, you are right. Arbitron uses Census projections to determine the population updates they implement each year in the Fall book. However, the Census data is supplemented and processed by Claritas (what used to be Market Statistics) to get a 12+ population for the metro. Arbitron's Metro Survey Area is not always the same as the OMB-defined Metropolitan Statistical Area, as the radio metro is defined in part by the amount of listening to local stations in outlying counties. In fact, many metros are redefined each year by Arbitron based on whether they get listening from the "main city" in significant quantity.
[/quote]OK, Detroit becomes number 11. So what? How does it matter to anybody who isn't a radio geek?[/quote]
Yes, station owners, managers and sellers... being in the top 10 means lots more national business than being outside the top 10. This could mean a million or two in annual billing for the leading stations.
Already Detroit bills like it were market 13 or 14, because it is perceived as a low growth market that is not "trendy" just like Cleveland or Pittsburgh or Buffalo.