From the Wikipedia page 
Metropolitan Manila (Filipino: Kalakhang Maynila) is the seat of government and one of the three defined metropolitan areas of the Philippines. It is officially known as the National Capital Region (NCR), and is commonly known as Metro Manila or simply Manila. It is made up of 16 cities namely: the City of Manila (the Philippine capital), Quezon City (the country's most populous city and former capital), Caloocan, Las Piñas, Makati, Malabon, Mandaluyong, Marikina, Muntinlupa, Navotas, Parañaque, Pasay, Pasig, San Juan, Taguig, and Valenzuela, as well as the municipality of Pateros.
The region encompasses an area of 619.57 km2 (239.22 sq mi) and has a population of 12,877,253 as of 2015. It is the second most populous and the most densely populated region of the Philippines. It is also the 9th most populous metropolitan area in Asia and the 5th most populous urban area in the world.
The region is the center of culture, economy, education and government of the Philippines. Designated as a global power city, NCR exerts a significant impact on commerce, finance, media, art, fashion, research, technology, education, and entertainment, both locally and internationally. It is the home to all the consulates and embassies in the Philippines, thereby making it an important center for international diplomacy in the country. Its economic power makes the region the country's premier center for finance and commerce. The region accounts for 37.2% of the gross domestic product of the Philippines.
The region was established in 1975 through Presidential Decree No. 824 in response to the needs to sustain the growing population and for the creation for the center of political power and the seat of the Government of the Philippines. The Province of Manila, the predecessor entity of the region, is one of the first eight provinces that revolted against the Spanish colonial rule in the Philippines at the end of the 19th century. Manila's role in the Revolution is honored in the Flag of the Philippines, where the sun's eight rays symbolize the eight revolutionary provinces.