It is often quoted that Nashville has more musicians per capita than
any other city in the U.S.  Is this just hearsay, or could you point
me to any verifiable data to back up this claim?  How would this
information be tracked and/or monitored?

If there is verifiable evidence, I would also be interested as to how
many are in New York and Los Angeles as well.  (Seconday music cities
such as Austin, Miami, Chicago, Seattle, San Francisco, Boston, and
others would also be good to know.)

I would imagine that this would be tracked by your Census Bureau in
the US based on what people claimed as there occupation (or
alternatley your tax offices).

You could take the occupation info and cross reference with population data.

Here are some links for the occupation codes:

http://www.census.gov/hhes/www/ioindex/ioindex02/occ02_m.html
http://www.census.gov/hhes/www/ioindex/ioindex02/txtnew02.html#2750
http://www.census.gov/hhes/www/ioindex/ioindex02/txtnew02.html#27-2042

You can download dataferret from the census bureau here so that you
can manipulate data:

http://www.thedataweb.org/download_ferrett.html

You can then use this program to build a spreadsheet to answer your questions.