Descendants of the High Line

If the High Line isn't already a New York icon, it's well on its way to becoming one. Since opening in June 2009, the park that runs for nearly a mile and a half through Manhattan's west side atop a defunct elevated rail line has attracted billions in new developments and legions of curious pedestrians. The park's second phase opened to much fanfare this June, and its first biography is due out in October. High Line: The Inside Story of New York City's Park in the Sky, written by Friends of the High Line co-founders Joshua David and Robert Hammond, even boasts a glowing blurb from Robert Caro — though he offered no insight into what Robert Moses would think of the park.

The High Line's success in New York has sparked a broader discussion about whether or not elevated parks can succeed in American cities in general. Witold Rybczynski, author of Makeshift Metropolis and professor of urbanism at the University of Pennsylvania, recently argued in The New York Times that great elevated parks require a "combination of history and density" unique to places like New York and Paris. (The Promenade Plantée in Paris, a precursor to the High Line, opened on a 2.8-mile viaduct in the 12th Arrondissement in 1993.) If too many cities try to duplicate the High Line concept in less ideal environments, then elevated urban parks will soon join the "dismal record of failed urban design strategies," Rybczynski wrote.