How did they form? What are their specific traits? Stereotypes (even untrue, if marked as such)?
If cultural differences coincide with geography, please mention in, too.
In the questions about weird things people from different continents do somebody pointed out, that Europeans have little knowledge of this, so please fix my ignorance.
It seemed every time we drove 100km, the yanks had a different name for cider (the alcoholic fermented drink, not fruit juice, although probably that too, seeing as "cider" sometimes meant nonfermented fresh fruit juice), a different name for fizzy drink and a different name for sausage… and so on. The boundaries were definitely not along state borders. Etymology maps of the US must look peculiar.