A large, densely populated urban area is called a metropolis. "She liked living in a metropolis because there were many opportunities in a city that were not available elsewhere, like 24-hour diners."
The noun metropolis comes from the Greek roots mētēr, meaning "mother," and pólis, meaning "city." Historically, the word referred to the founding city-state of a region in Ancient Greece. Today the word refers to any urban area. The largest metropolis in Massachusetts is Boston, which is also the capital. Sometimes people use the word metropolis ironically or sarcastically: "She came from the booming metropolis of Tumbleweed, population 325."