“[...] through the Black Belt up to North Carolina, [...]” When I saw that section of the map, before reading your comment, I thought “Bible Belt” and “Hurricane Border” – the latter of which is more interesting to me. Florida gets hit by pretty much every hurricane that comes along, so the people who live here need to be able to afford the repairs and such, and we also have a lot of tourism and ‘snow birds’ that keep the economy up (in fact, those are the main businesses in many areas, along with farming). But that string of blues looks like the area where hurricanes hit with less frequency, possibly not enough that preparation is given much thought, but enough to still have an economic impact.

As for the bible belt one, I went to check my estimate of the area, and found another map set you might be interested in:
http://www.valpo.edu/geomet/geo/courses/geo200/religion.html

There are several maps linked on that page, from 2000 survey data, and I found these quite interesting:
Religious Adherents (%) in an area: http://www.valpo.edu/geomet/pics/geo200/religion/adherents.gif
Leading Church Bodies in an area: http://www.valpo.edu/geomet/pics/geo200/religion/church_bodies.gif

And, most interestingly:
Catholics (%): http://www.valpo.edu/geomet/pics/geo200/religion/catholic.gif
Baptists (%): http://www.valpo.edu/geomet/pics/geo200/religion/baptist.gif
- The areas are almost completely opposite!