1) Merge the Texas Triangle and Gulf Coast into a single mega-region, which is not unreasonable at all if Minneapolis and Pittsburgh can be considered part of the same mega-region. Houston is really the linchpin between the two regions in the same way Chicago is between those two, or NYC is between Philly and Boston – any split just doesn’t make sense.

2) Since Katrina and the depopulating of New Orleans, I think there’s a fair argument for dropping the concept of a Gulf Coast mega altogether, since, without Houston, they are a string of relatively smaller metros that would not even come close to ranking on your list. If places like St. Louis, Kansas City, Memphis, Nashville, Las Vegas, and Salt Lake City/”Wasatch Front” (comparable to Denver) can be left out of regions, then I don’t think Mobile, Pensacola, Gulfport, Baton Rouge, or NOLA have much of a case, relatively speaking.

Underscoring Richard’s point in the comment above — we think highly of the RPA’s work and our light-based approach has its basis in the mega definitions that came out of their multi-factor approach (along with Lang’s, etc.). We saw that we could identify essentially the same set of US megas using contiguous development as a proxy for integration and found that it worked remarkably well. Because the approach was so simple and objective, we could then extend the same approach to the rest of the globe. It would be really, really hard to extend the RPA’s approach to the the globe — yet this seems to be a scale where mega-regions are particularly useful abstractions.

With regard to Texas, it is worth noting that the RPA places Houston in _two_ megas — the Texas Triangle and the Gulf Coast. It is the only city in the US that the RPA classifies as part of two megas. They have some very pretty maps here:

http://www.america2050.org/pdf/America2050prospectus.pdf

Check out the US map that spans pages 10 and 11.

Our emphasis on contiguity grouped Houston unambiguously with the Gulf, but the overall picture is not radically different. A Houston city planner would be foolish to start ignoring Dallas based on our maps, but nobody thinks they should forget that they are part of the Gulf Coast.

Of course, those regional social connections often lead to business connections, thus interlinking that regional economy over time and validating the mega-region concept.

One issue with this phenomenon is that it often stops at a national border for obvious reasons (with maybe the European Union being a recent exception, because of the new ease crossing borders and gaining employment there), thus the comments questioning regions crossing the Canadian border.

Even with that, I’m actually surprised there is continuous light between Houston and NOLA, because there’s mostly a giant swamp in southern LA, including a 35+ mile continuous bridge (“Atchafalaya Swamp Freeway”) over the empty swamp on I10 between Lafayette and Baton Rouge.

On the other hand, there is little incentive for people to live on the nondescript land between Houston an the other Texas Triangle cities, but there is certainly a tremendous amount of daily traffic between those cities – car, truck, and plane. Check out the mapped flows on p.8-9 of this report on the Texas Triangle:
http://www.rpa.org/pdf/temp/America%202050%20Website/Healdsburg_Texas_pp_21-36.pdf

The reason the light looks more continuous between San Antonio and DFW is that that’s the edge of the Texas Hill Country, which is a much more attractive area to homestead. Most retirees or others who want to “move to the country” in Texas go there, supporting many small towns along I35.

There are certainly energy ties between NOLA and Houston, and maybe that justifies extending the Texas Triangle mega-region east to include NOLA, but it doesn’t make sense to cut off Houston from the rest of the Triangle just because few people choose to live in-between.

Of course the best would be AmTrac if it had a reasonable schedule, didn’t get sidelined or break down regularly. A Cascadia high-speed rail would probably be the most productive thing for creating a coherent region here.

The hardest part by far was developing these geographic boundaries and creating techniques to estimate economic activity based on light emission. The next steps are easier.

An alternative, and also very interesting method, for identifying regional locations of economic activity, based on “gross cell product” has been proposed by William Nordhaus and his team at Yale. So progress is being made.

Mega-regions are a big project of the Prosperity Institute, so expect more to come. And expect that some of the issues everyone is raising here to make it into the pages of Who’s Your City.