Medan is the capital and largest city of the Indonesian province of North Sumatra. A regional hub and financial centre of Sumatra, it is regarded as one of the four main central cities of Indonesia, alongside Jakarta, Surabaya, and Makassar. Medan has a population of over 2.2 million within its city limits, and over 3.4 million in its built-up urban area, making it the fourth largest urban area in Indonesia. The Medan metropolitan area—which includes neighbouring Binjai, Deli Serdang Regency, and a part of Karo Regency—is the largest metropolitan area outside of Java, with 4.6 million residents. Medan is a multicultural metropolis and a busy trading city bordered by the Strait of Malacca. A gateway to the western part of Indonesia, Medan is supported by the Port of Belawan and Kualanamu International Airport, both of which are connected to the city centre via toll road and railway.