Is the New York mayor the most powerful in the world?
The race to succeed Michael Bloomberg as mayor of New York is well under way. Awaiting the winner is an international profile and a budget of $70bn (£45bn). So how does the job compare with mayors of other big cities?
The new occupant of City Hall on Manhattan's Broadway will have more money to spend than a small country - and a population to match.
So perhaps it's no surprise that when the identity of New York's next mayor is revealed in November's election, it will make news around the world.
He or she will probably be the most powerful mayor on the planet, says Mitchell Moss, professor of urban policy and planning at New York University, because the job comes with unique executive powers - hiring and firing the people heading the city's key agencies like police and schools, while also setting the budget.
"The California governor doesn't even have that power. And the mayor controls the education of one million children. Education around the world is usually a national responsibility and not a city governor responsibility."
It's power that has come incrementally, ever since the British drove the Dutch out and gave the city control of its waterfront in the 17th Century. A recent addition came in 2002 when the vast schools system was reconfigured and made directly accountable to the mayor.
The person heading the largest city in the US has often enjoyed an international profile. Ed Koch - who ushered in the city's boom and put the near-bankruptcy of the 1970s behind it - was often photographed riding the subway or walking the streets.
And after 9/11, the no-nonsense figure of Rudy Giuliani came to represent the city and the country at its time of need.
But these days, it's a job that doesn't hog the international stage on its own. The ever-quotable London Mayor Boris Johnson appears on primetime US television, and his predecessor Ken Livingstone struck a controversial oil deal in Venezuela with Hugo Chavez.
The mayor of Paris, Bertrand Delanoe, drew praise for a free bike scheme which has been copied elsewhere. And the Olympic spotlight has now moved from Johnson to Rio's mayor, Eduardo Paes.
"Mayors without question are very much consistent with the spirit of the age - visible, figurehead urban leaders who are a much better fit in a world of 24-hour news and the need for celebrity visibility," says local government expert Tony Travers of the London School of Economics.
Bloomberg's forays into public health - the bans on smoking and trans-fats, and attempts to limit fizzy drink sizes - have inspired mayors the world over to intervene in health without fear of being accused of nannying, he says.
In the UK, cities like London, Bristol, Liverpool and Leicester have begun to adopt - with varying levels of public interest, admittedly - the American model of a directly elected mayor, and the same has happened in German and Italian cities. Dublin could be next.
But who is the most powerful? The New York mayor spends more money than London's, where much of the power is devolved to the 32 London boroughs (plus the City of London), including schools. But Bloomberg has little say over transport.
Mayors who act as state governors are more powerful than Bloomberg but none has his influence, says Tann vom Hove, a senior fellow at the City Mayors Foundation, an international think-tank.
"The previous mayor of Mexico City [Marcelo Ebrard] legalised abortion and introduced gay marriage, things the mayor of New York can't do. And the Berlin mayor can block federal legislation."
But there's a difference between the job description and the man, says Vom Hove. Bloomberg has probably been the most influential mayor through his personality and wealth, and it's unlikely the person that follows him will match that.
Another candidate for "most powerful" city leader is Tokyo's governor, Naoki Inose. He is technically not a mayor, he acts as chief executive of the Tokyo Metropolitan Government, which is responsible for transport, secondary schools, hospitals, economic development, sewage and disaster management.
His budget of £41bn ($63bn) is nearly the same as Bloomberg's but his powers are more far-reaching and he governs twice the number of people.
Plus, according to the Japan Local Government Centre in London, only 7% of his revenue comes from central government, the smallest proportion compared to any other world city, including New York which receives 31% of its cash from federal sources.
Many mayors operating on much smaller budgets have left their mark on history. Teddy Kollek, who served as Jerusalem mayor for nearly 30 years, was described as the most influential Jewish builder of the city since Herod the Great in Biblical times.
And Pasqual Maragall was one of a succession of mayors in Barcelona who transformed the city in the post-dictatorship era.
Mayors can be more effective than national politicians because there is less posturing, says Travers. If you govern a city of 10 million people, you have to make sure everything is working and the police are on the streets. They're not highly political acts, they're done by Conservatives, Labour, Republicans, Democrats and Socialists in the same way.
Political theorist Benjamin Barber takes this argument a step further in his book, If Mayors Ruled The World, in which he says mayors are far better at addressing global issues than heads of nation states.
Countries are dysfunctional in global relations, he argues, because they're walled states with borders strengthened by sovereignty and national culture.
"National political figures adhere to great historical norms and political ideologies but mayors have to fix things - they have to pick up the garbage and fix the sewer. They're problem solvers and that's what makes them pragmatic."
Cities already co-operate across borders, he says, either one on one or through global networks like the C40 network to tackle climate change.
And now that a majority of the world's population is found in urban areas, perhaps this will be the century of the city - and the mayor.