San Diego is seventh largest city in United States of America, and 2nd largest in California, holding a population of over one million residents and approximately two million in the surrounding metropolitan area, which is mainly made up from San Diego County.

Chicago is the third-largest populated city in the United States and the largest inland city nationally. When combined with its suburbs and eight surrounding counties, the greater metropolitan area known as Chicagoland, concentrates more than 9 million people. Such high density of population also shows greater number of ageing population, baby boomers and steady increase [...]

In United States of America, Houston is the fourth-largest city nationally and largest city in Texas, covering an area of 579 square miles (1,500 km2). The city also holds a population of 2.1 million people.