Johannesburg, colloquially known as Jozi, Joburg or "The City of Gold", is the most populous city in South Africa. The City of Johannesburg itself has a population of 5,538,596, while the City of Johannesburg Metropolitan Municipality has a population of 6,599,190, making it one of the 100 largest urban areas in the world. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, and seat of the country's highest court, the Constitutional Court. Situated on the mineral-rich Witwatersrand hills, the city has long been at the epicentre of the international mineral and gold trade. The richest city in Africa by GDP and private wealth, Johannesburg functions as the economic capital of South Africa and is home to the continent's largest stock exchange, the Johannesburg Stock Exchange.