Johannesburg, also known as eGoli, is the most populous city in South Africa. The city is affectionately known as "Jo'burg", "Jozi" and "JHB" by South Africans. Johannesburg is the provincial capital of Gauteng Province, the wealthiest province in South Africa, and the site of the South African Constitutional Court. The city is one of the 40 largest metropolitan areas in the world, and Africa's only officially designated global city (classified as a gamma world city). Whilst sometimes mistakenly assumed to be South Africa's capital city, Johannesburg is not even one of South Africa's three official capital cities (although Pretoria, which is in the same province, is).
Johannesburg is the site of a large-scale gold and diamond trade due to its location on the mineral-rich Witwatersrand range of hills. Johannesburg is also served by O.R. Tambo International Airport, the largest and busiest airport in Africa and a gateway for international air travel to and from the rest of southern Africa.