But if the park is a unique lens on the city, it's also a showcase for the work of its lead designer, Corner - a pugnacious Englishman who is now making a park out of an 890-hectare landfill site on Staten Island and designing the 37-kilometre-long Lake Ontario Park on Toronto's waterfront. He's a star in a profession that most people don't understand.
"Landscape is plagued," he says. "You're working with a natural medium, so the genius of artistry and design is often not apparent. Central Park is a classic case in point. People will visit and think it's kind of natural. But it was shaped, it was earth-engineered. Everything in there was designed with a certain artistic vision - which was pretty radical in the 19th century."
Corner's work, like Central Park's Frederick Law Olmsted's, is groundbreaking. A generation ago, cities and planners would have looked at a rail line like this and done one of two things: "Preserve it and make fake history," as Corner puts it, or bring in the wreckers.
The High Line's in-between approach reflects a new set of ideas among landscape architects, who are focusing their efforts on the scars in the fabric of cities - like garbage dumps and railway lines. The park is an instrument to remake the city, aesthetically, environmentally and culturally. "Traces of the old are still evident: the old historical railings, the grassy landscape, the views across New York," Corner says. "But there's also this new landscape and this new social program on top of it."
David saw some of the transition from old to new. In the 1990s, he was a journalist living in Chelsea, the old manufacturing district that was becoming the city's art gallery hub. The High Line was barely visible, sticking out over a street here and there. "It was easy at that time to assume that those little pieces were just remnants," he remembers. But he started digging, and met a neighbour, artist and entrepreneur Robert Hammond, who shared his interest. Eventually the two made the High Line their cause, fighting to save it as Rudy Giuliani's administration moved to have it condemned.
At the same time, this part of the city was rapidly changing. Chelsea was a flashpoint in the bubbling global art market, and the Meatpacking District adjacent to it was becoming a hub for clubs and restaurants. "This, early on, was designated as a nightlife ghetto," hotelier André Balazs says. "There were absolutely no residents around here, and that's how the police wanted it." Suddenly the slaughterhouses were cheek-by-jowl with celebrity hangouts like Pastis and then two hipster-central hotels, Gansevoort Hotel and Soho House.
Balazs wasn't there first - but his hotel, the Standard, would wind up literally on top of the High Line, a chevron-shaped tower teetering on concrete stilts over the park's southern end. "When we started, it wasn't clear there was going to be a High Line," he says, sipping ice water in the garishly red café of his new hotel. Yet as he started creating the Standard, he became one of the park's patrons, and twisted his development project to fit around it.
"Most landlords and developers thought of the High Line as something that had negative value," he recalls, sitting in a 1950s-vintage Arne Jacobsen armchair. "The usual arguments were: How am I going to develop my land when I've got a railroad running through it?"
And then Friends of the High Line, David and Hammond's little project, started to win. Driven by the help of designer von Furstenberg and other celebrity supporters - actor Ed Norton is a long-time advocate - it picked up speed and money, becoming a partner with the city in launching and maintaining the park. They raised $49-million of the first leg's $169-million price tag. All their work, and the whiff of an avant-garde new park, only stirred up the rush of designers, developers and high-end retail, which carried on right into last fall's market crash. (Some of the condos are still going up.)