So,
Enable these two mods (and the map itself as well should be enabled obviously):

"InGameMaps [Main]"
"InGameMaps {S. Korean Downtown "Sema"]"

Both of them should be enabled at once, and as I udnerstand, that "Sema New city" map mod gets activated automatically as well, when you enable these 2 mods, but make sure it's also enabled for sure.

Then it should work. Not only the "main" version of in-game map mod is needed for such maps, but also you should enable the sub-mod for the workshop map you're going to be using, and in this situation - "S. Korean Downtown "Sema" is the SUBmod wich you gotta enable along with the "main" submod, together.