Johannesburg was a city in South Africa, in the Transvaal province. It had been visited at some point by the Doctor, and the Third Doctor said that he intended to someday return to it. (PROSE: Last of the Gaderene)
At some point in the history of the city, racial tensions between black and white humans had erupted into violence. (PROSE: Infinite Requiem)
Individuals
Torrance Hayton, as Trey later found out, was from Johannesburg. (PROSE: Instruments of Darkness)
Brockie was from Johannesburg, and thus spoke fluent Dutch. (PROSE: Players)
Bliss was from Johannesburg. (PROSE: Last of the Gaderene)