Twelve years ago the term "Bilbao effect" was coined in response to the swarms descending on the Spanish city of Bilbao--previously known as the Pittsburgh of Spain--to see the titanium swirls built by Frank Gehry for the Guggenheim Museum . Until then most of us had never heard of Bilbao; we weren't even sure how to pronounce it. But in its first year the Guggenheim logged 100,000 visitors. Since then it has clocked close to a million a year, and its annual impact on the local economy is worth about $147 million.
Not surprisingly a rash of cities tried to copy the Bilbao Effect for their own economic benefit. The Milwaukee Art Museum  opened an addition by Santiago Calatrava  with a giant retractable sun shade; Seattle built the Experience Music Project  by Gehry and San Francisco remade its de Young Museum  with Herzog & de Meuron (above), to new a few.
Now parks may be replacing culture as the design destination of the day. The High Line , a half-mile stretch of elevated highway landscaped after years of abandonment, opened in the West Chelsea neighborhood of Manhattan this summer to a delirious response. More than half a million people visited the High Line over its first two months. New York officials estimate that the park will bring the city $900 million in revenue over the next 30 years.
"The surge in development spurred by the High Line is the latest exhibit in the growing stack of evidence that having beautiful, well-maintained parks is much more than a nice amenity cities can ignore when times are hard," Anne Schwartz wrote at the Gotham Gazette .
Even before the High Line opened in June a corridor of new residential towers and offices had gathered around it, representing a total of $4 billion in private investment. The new developments includes a 21-story residential tower, known as "the Vision Machine ," designed by French architect Jean Nouvel and a condo complex  by Annabelle Selldorf.  The new Standard Hotel  by the Polshek Partnership  straddles the High Line, and at the south end a branch of the Whitney Museum by Renzo Piano  is planned for 2012.
The High Line isn't the only new park to draw a crowd. Two miles to the north the city closed off traffic on two sections of Broadway, creating a public pedestrian space  around Times Square initially furnished with 376 beach chairs. As far as I know, nobody has studied the drawing power of the new public space, or its financial benefit, and it might be hard to analyze given the hoardes that pass through Times Square. But it's clear that the instant park, like the High Line, had the kind of gleeful public sensation that a few years ago would have been reserved for the opening of museums and other cultural institutions.
The new Times Square may not be quantifiable, but the American Planning Association  is studying the economic benefits of other open spaces and parks around the country: A greenbelt in a Boulder neighborhood adds $500,000 in property tax revenue annually, for example, and the East Bay Regional Park District in Oakland stimulates $254 million annually in park-related purchases, $74 million of which is spent in the local East Bay economy.
We may now be returning to the conviction that Frederick Law Olmsted started with 150 years ago: To justify the expense of Central Park, he charted the value of real-estate fronting the park Between 1856 and 1873. He found that over that period property adjacent to the park increased in value by $209 million.