Did I miss it or is there no methodology description justifying how they reached this?
If there was some good standard survey on cultural views, you could compare geo regions on the summary stats of their responses, and cluster them. But you'd need a _huge_ number of responses to get good county-level data. And then I think we'd expect to see lots of county-to-county differences reflecting the urban-rural contours, immigration differences tied to industry, etc, rather than these big, uninterrupted regions. E.g. I would think King County, WA and Alameda County, CA have a lot more in common with each other than either does with Del Norte County, CA.
If there was some good standard survey on cultural views, you could compare geo regions on the summary stats of their responses, and cluster them. But you'd need a _huge_ number of responses to get good county-level data. And then I think we'd expect to see lots of county-to-county differences reflecting the urban-rural contours, immigration differences tied to industry, etc, rather than these big, uninterrupted regions. E.g. I would think King County, WA and Alameda County, CA have a lot more in common with each other than either does with Del Norte County, CA.