05. Manila, Philippines Urban Area: 21.9 million people
City: 11.8 million people
Manila's colonial past is reflected in its architecture. Intramuros, the historic center, is surrounded by a massive wall built by the Spanish in the 16th century. Its parks and historic buildings have become a major tourist attraction.
Urban Detail — More than 3 million people in Manila live in slums without electricity, sanitation, and access to drinking water. Population density is extremely high, in some areas more than 100,000 people live on one square kilometer. (Source: Reuters)