Karachi is the largest and most populous city in Pakistan and 7th largest urban city in the world. Karachi is the capital of Sindh province. Ranked as a beta world city, the city is Pakistan's premier industrial and financial centre. Karachi is also Pakistan's most cosmopolitan city. Situated on the Arabian Sea, Karachi serves as a transport hub, and is home to two of Pakistan's two largest seaports, the Port of Karachi and Port Bin Qasim, as well as the busiest airport in Pakistan. Karachi collects over a third of Pakistan's tax revenue, and has a formal economy estimated to be worth $78 billion as of 2008, although the city's large informal economy is not reflected in GDP estimates, and employs up to 70% of the city's workforce.