Cities are important centers of population, culture, business, and transportation. Some cities have grown into massive urban areas with tens of millions of residents. Population size is often used to compare cities, although rankings may vary depending on whether city proper, urban area, or metropolitan area populations are measured. Tokyo in Japan is widely recognized as the world's largest metropolitan area by population. The city is known for its advanced transportation system, technology, and economic importance. Tokyo's metropolitan region includes many connected urban districts that together form a huge population center. Delhi, the capital region of India, is one of the fastest-growing major cities in the world. It serves as an important political, cultural, and economic center. Rapid urbanization and migration have contributed to its large population. Shanghai, located in China, is another highly populated city. It is a major global financial hub and one of the world's busiest ports. The city's economic opportunities attract people from across China and beyond. Dhaka, the capital of Bangladesh, has experienced significant population growth over recent decades. It is the country's main center for government, industry, and commerce. High population density is one of its defining characteristics. Other highly populated cities include São Paulo in Brazil, Mexico City in Mexico, Cairo in Egypt, and Beijing in China. These cities play important roles in their countries and regions. Large cities often face challenges such as traffic congestion, housing shortages, pollution, and pressure on public services. However, they also provide opportunities for employment, education, innovation, and cultural exchange. Urban planners work to improve transportation, housing, and infrastructure in growing cities. As global urbanization continues, many of the world's largest cities are expected to grow further, especially in Asia and Africa. Understanding population trends helps governments and organizations plan for future needs and sustainable development.