More than eight million people live in New York, the most densely populated city in the United States. It is also a city of enormous diversity. People of every economic class live alongside each other. New immigrant communities meld into old ethnic enclaves.

"Cannelloni, manicotti, lasagna, ravioli, spaghetti marinara, $6.50. Would you like to come inside and try it?" says a waiter inviting customers into his restaurant in Little Italy.

A century ago, these streets overflowed with Italian immigrants. Originally from southern Italy, they brought their traditions with them, creating a vibrant neighborhood known for its authentic cuisine and outdoor festivals.

Now, Little Italy spans just a couple of city blocks. It mostly attracts tourists, who sample rich pasta dishes, delicate cheeses, sweet pastries and cappuccinos, coffee made with steamed milk.

In 1910, half-a-million Jewish immigrants from Eastern Europe lived directly next door in what was the most crowded spot on earth.

The story of Italian and Jewish communities in Manhattan's Lower East Side illustrates the changing face of New York neighborhoods and neighborhood borders.

Today, the Lower East Side remains a crowded ethnic enclave. But it has changed with U.S. immigration patterns. Now, demographers say, at least 300,000 Chinese immigrants live there.

Historian Joyce Gold gives walking tours of the neighborhood, which is part of a growing Chinatown.

"To me, the speed at which some of these blocks have become Chinese is the same speed that in the 1850s the blocks became Irish," she explained. "In the 1890s, they became Eastern European. To me, it is something of a window into the past. Very suddenly, the language is different, the cuisine is different, the sounds are different. But in some ways, nothing ever changes in New York."

Residents push their way through Chinatown's outdoor markets. Cashews and walnuts, soy and rice products are for sale at low prices. Exotic fruits and vegetables tumble off counters. Colorful fish are packed on ice, and a strong smell permeates the air, as workers sweep away discarded fish parts. Sipping a tropical Thai drink, served in a coconut, one Chinese-American tourist says the architecture, the pollution and the sounds remind her of China.

"It is pretty much like this," she said. "It feels like China - the people, the merchandise, the traffic."

Stories are told of aging Italian-American musicians playing at Chinese-American funerals.

The transition has not always been easy. Most second and third generation Jews and Italian-Americans moved to more affluent neighborhoods decades ago. But some of those who remain resent the infusion of the latest wave of immigrants.

"It was nice," commented one Italian-American resident. "It was all Italian, [there were many] families. There is not that much around here anymore, except for a few blocks of restaurants. It was better the other way."

Immigration patterns are not the only force of change in New York's neighborhoods.

"It's supposed to be the hot [trendy] neighborhood," said Stephen Downes, gallery-owner, who is one of many artists, who are opening shops on the Lower East Side. "About eight years ago, they said this was the neighborhood to be in. I was looking to open a gallery, so I found this place."

Historian Joyce Gold says artists and young people are often the harbingers of change. They are willing to cross borders for more space and lower rent.

"I think it was the building right around the corner, started to have a skylight put in, a larger window facing north," she said. "To me, that was the beginning of the change 15 year ago, because northern windows are often punched in for artists who want northern light."

In fact, rising rent prices have caused borders to fade throughout the city.

Borders are blurring between Latino's and African Americans in New York's Harlem and the posh neighborhood to the south.

Cuban bakery-owner Jose Ramirez says the disappearance of informal borders, which used to be around 96th Street, is pushing many Latinos out of Spanish Harlem.

"Ninety-sixth Street used to be the cutoff," said Mr. Ramirez. "Not only in the type of people that were there, but also in the rent that was charged for apartments and businesses. That is no longer the case. I would say, in the last 10 years, it has been erased, mostly. Rents around here [above 96th Street] are incredibly high now. Everything is going up, and the people who are here, are being forced out, basically."

High rents are driving many immigrants to the suburbs, where ethnic communities are increasingly common. But regardless of why they leave, many immigrants return to visit the old neighborhood with their children, to taste the foods and maintain a connection to their past.