Karachi (Sindhi: ڪراچي, Urdu: کراچی / ALA-LC: Karācī IPA: [kəˈrɑːˌtʃi] ( listen)) is capital of province Sindh as well as the largest and most populous metropolitan city of Pakistan and the main seaport and financial centre of the country. Karachi is also known as City of Lights mainly due to city's night life, for which it is famous as the city which never sleeps. Karachi metro has an estimated population of over 23.5 million people as of 2013, and area of approximately 3,527 km2 (1,362 sq mi), resulting in a density of more than 6,000 people per square kilometre (15,500 per square mile). Karachi is the 2nd-largest city in the world by population within city limits, the 7th largest urban agglomeration in the world and the largest city in the Muslim world. It is Pakistan's centre of banking, industry, economic activity and trade and is home to Pakistan's largest corporations, including those involved in textiles, shipping, automotive industry, entertainment, the arts, fashion, advertising, publishing, software development and medical research. The city is a hub of higher education in South Asia and the Muslim world.