"Uptown" v. "downtown" w/meaning: "main shopping district"

[Wilson Gray]

In Marshall, Texas, my birthplace, the county courthouse stands on the
highest point in town, facing the main shopping district, which is
referred to as "uptown" by the locals. Everyplace else that I've ever
lived - various places in Missouri, California, Illinois, &
Massachusetts, the main shopping district is referred to as "downtown."
So, wrt Marshall, it's obvious that downtown is referred to as "uptown"
because it quite literally is _up_town, as any fool can plainly see.
However, an article in the NYT Travel section noted that, in
Charleston, SC, too, downtown is referred to locally as "uptown," but
provided no further information. Does anyone know how the Charleston
usage came to be?

-Wilson Gray