These boundaries are determined by commuting patterns.  So some metros have massive MSA and CSA boundaries for the fact that they are the dominant economic force in the region...meaning that the surrounding areas depend on this job/economic base for their own vitality.

 

Before I start searching, does anyone know if this underlying "commuting patterns" data is available anywhere on the web? I would be interested in taking a look at it just to balance against my anecdotal experience. I know (and have run into) many people who are commuting to the Cleveland CSA daily for work that live outside the CSA. From Mahoning, Ashtabula and Erie -- I've run into three people from Erie County in the last two weeks alone. Just curious what the actual numbers might be.

You can get all the county-to-county worker flow data here: http://www.census.gov/population/www/cen2000/commuting.html

 

That's from the 2000 census.  Although the latest metropolitan area definitions are newer than that, I assume they're based on the 2000 data.

I think the Columbus CSA is in the 6000+ range. I did some stuff a couple of years back but i lost most of my bookmarks when i upgraded my computer. The list above is CSA's i think. That's why area's that only have an MSA like Phoenix, Portland, etc are missing.