Learned discourse from barbecue authority and UNC sociology professor emeritus John Shelton Reed, on the styles of barbecue sauce in use in South Carolina:
* The vinegar and pepper region covers the eastern quarter of the state. This is “a southward extension of eastern North Carolina-style sauce,” states Mr Reed.Strange Maps #246: Southern Sauce Sources
* “The tomato region ditto for North Carolina’s Piedmont- or Lexington-style sauce, which is basically the eastern sauce with a little tomato added, still thin and vinegar-flavored.”
* The ketchup region is influenced by what they serve in Georgia “and most of the trans-Appalachian South – or for that matter in grocery stores – a thick, sweet, ketchupy sauce.”
* Unique to South Carolina, though, is “the mustard sauce of central South Carolina, (which) is unique to that state, and (which) gives it more distinct barbecue regions than any other.”
Delightfully, a commenter in the thread at Strange Maps made an appropriately-colored Google Maps overlay of the South Carolina Sauce Map.
See here for the North Carolina Google Sauce Map.
And there's much discussion, in the comments, of where the precise dividing lines are.
Barbecue is serious business.