David, I don't think that its as simple as "brain drain." I think that there's a general pattern of migration from smaller places to cities. I've been looking at this map of migration patterns and even in popular places like CA and WA the rural counties are losing population while cities gain (I was looking at migrants age 25-29: my guess was that people who move at this age are doing so for work/ to settle down in a desirable place, after college/grad school). Even Des Moine and Souix Falls had relatively big gains of young migrants while the rest of their states lost population.

I think that Michigan has been especially hard hit because of its dependence on skilled manufacturing jobs that have been lost to outsourcing and automation, and that the old narrative writing off the Upper Midwest (and we need better names - Great Lakes States and Great Plains?) is flawed.

I believe I like to see map data in shorter increments over the time period from 2000 to 2015 in 5 year blocks. Such as 2000 to 2005, 2005-2010, 2010-2015 or something close to that would show shift dynamics. I had seen some recent migration patterns showing data from 2005 and later and some of the patterns are different. In some narrower resolution of data as you pan through the years, I notice some significant movement both to big cities (because of jobs) but also more bigger dynamics to lesser regulated and less expensive areas. Texas would look hotter. Florida is hot and had been before the recession and continued to be because land is cheap and is not heavily regulated. Texas had seen some hot development and migration to that area because in Texas, it is a land of minimal regulation.  Again, it had been centrally located around where the jobs are. In California, you'll notice the hot housing development is not in Los Angeles. People are migrating to new developments out in the suburban sprawl of L.A. metro area that is outside the county. Riverside and Pasadena. Since, L.A. county core area had been developed already but it gets more expensive so people on more modest income are pushed out because of the cost of living in the core so they commute longer and longer distance. This is of course broad picture and reality is more complicated. The picture show people are obviously looking to less costly places to live but close enough to work where the jobs are. Since these are actually diced up into counties, I can tell you most of San Bernadino & Riverside counties development and population is on the western half of it. You are also seeing moderate migration trend to Kern county and San Luis Obispo counties. That's where you are going to find new housing tracts because there isn't much virgin land is Los Angeles county to develop. The map only gives so much information but you can extrapolate some of what I said from the general peripheral information available online. Los Angeles metro area as with all big cities are hot places for jobs but from housing perspectives, but you can see from the map, Los Angeles county core is huge and encompasses the county but it is also progressively more expensive and the sprawl trend had been happening outside L.A. county, even when I last lived there 20+ years ago. I can just people getting jobs in L.A. but getting a home in say San Bernadino and Riverside and just commute in to work. 

In some areas on the map, the population growth trend is high BUT the population is low so it really doesn't necessarily show a huge migration. 

This like below might be an interest and you can look at how each state grow or shrink based on population but net migration is positive, the population is growing. When it shrinks, there is a net migration away from the state (shrinkage of population). It would been nice if it could show this at county level but okay.

http://www.ravi.io/us-population-trends-cartogram.

Similar cartograms for each state at county level resolution probably exists and looking through each of them can give an interesting picture.

This one might be interesting in sensing how population is moving.

http://homepage.ntlworld.com/keir.clarke/leaflet/cities.htm

and just out of interest or curiosity:

http://www.forbes.com/special-report/2011/migration.html

Each map or cartogram or whatever tells slightly different things.

In the Forbes link, the primary source for inbound migration for the L.A. county from New England/New York area. San Bernadino and Riverside also gets a chunk of people from those states but they get alot of people exiting the core L.A. and Orange County and even San Diego county to that area with the suburban sprawl. 

People are leaving the area typically to less expensive areas where they can utilize the value of their California property to buy a bigger piece of land and house or even build a bigger house for than the property they have. It's all exchange of equity. What your money can buy in different areas. 

There is interesting data to show generally where people are coming from and going to.

Ok, thanks for the correction.