PARIS -- When visitors to Disneyland embark on the 15-minute intercontinental expedition around the Seven Seaways canal, few, if any, are likely to have a world exposition on their minds. But it was for the 1964 New York World's Fair, as the expo was known, that Walt Disney designed the "It's a Small World" boat ride.
The Eiffel Tower and the Atomium in Brussels are other lasting legacies of the world expos that have showcased the latest in technology, architecture and culture every five years since London's inaugural Great Exhibition of the Works of Industry of All Nations in 1851.
Today, though, hosting an expo means much more than building things. Would-be bidders count on an economic boost and a higher international profile as benefits from staging the event.
But on the negative side, they are also faced with a series of challenges, like ballooning costs and an uncertain future for some of the large scale construction that such events leave behind.
Still, the race for the 2020 World Expo, the next to be awarded, has attracted a diverse group of cities, all situated in emerging regions: Dubai; Izmir, Turkey; São Paulo; and Yekaterinburg, Russia.
"An expo marks a certain 'coming of age' for a city," Urso Chappell, an expo historian, said. "It can aid a city's physical redevelopment as well as the nation's image abroad."
For the 2020 bidders, then, the event means more than hosting more than 200 nations and their pavilions for six months.
Much like the Olympics or the soccer World Cup, an expo brings a host of economic opportunities for a city: Jobs are created as large construction projects get under way, and international and local tourism grows, giving a boost to restaurants, hotels, car rental agencies and other businesses. The Dubai bid, for instance, anticipates more than 25 million visitors and 270,000 new jobs because of the expo.
At the same time, though, much as with any other global mega-event, expo organizers have to walk a tightrope, balancing cost and legacy.
The Shanghai World Expo 2010, for example, cost the equivalent of $4.2 billion, according to government figures. But the Chinese news media have reported that the actual cost of staging the event was north of $50 billion -- more than was spent on the Beijing Olympics in 2008.
The Shanghai Expo has also left a number of "white elephants," venues and construction that proved useless after the event and were abandoned. Some, like Germany's pavilion at the expo, were razed.
The hosts of the next world expo, which will be held in Milan in 2015, hope to avoid the same fate by "organizing a totally sustainable event and building the country pavilions with eco-friendly materials which, if necessary, can be easily dismantled at the end of the six-month event," said Giuseppe Sala, chief executive of the Expo 2015 Co.
One of the few things that will remain after the Milan Expo will be a large park. The organizers say plans call for 56 percent of the site to remain "green" after the event. At $1.7 billion, the projected investment by the Milan Expo would also be much smaller than Shanghai's.
With a reasonable budget and a sound legacy plan, a world's fair can become a transformative opportunity for a city, and even for a country, expo officials say.
"For the hosts, expos are a key part of a strategic plan for urban development and act as catalysts for accelerating infrastructural transformations," said Vicente Gonzalez Loscertales, secretary general of the Paris-based Bureau of International Expositions, which chooses the host cities and supervises the events. "At the same time, the expo has more intangible but equally powerful impacts on the branding of the city and of the country, and on their international image."
It is exactly that "unique P.R. opportunity," as Mr. Gonzalez Loscertales calls the expo, that the 2020 bidders are looking to exploit.
Dubai, which would become the first host of a world's fair in the Middle East, has emerged as the front-runner, boasting the biggest financial and governmental support. On the other hand, political tensions in Russia, most recently over what is viewed as an anti-gay law, and in Turkey could hurt the chances of Yekaterinburg and Izmir. São Paulo, the largest city in the Southern Hemisphere, is seen as least likely to succeed when the 100 or so delegates of the exposition bureau's General Assembly vote in November, people familiar with the bidding process said.
The fact that all of the 2020 bidders come from emerging markets is indicative of the changing landscape of international relations. More and more nations use such global events to elbow their way onto the world stage.
"Shanghai 2010 is a perfect example of an expo held to show that a country is an important international player," Mr. Chappell, the expo historian, said. It sent a "statement to both other countries and its own citizens that China had arrived on the global stage."
Held on the heels of Beijing's grandiose 2008 Summer Olympics, the expo was the most heavily attended in history, with a record 246 participating countries and organizations as well as 73 million visitors.
"An expo allows a city to display its organizational capacity, hospitality and culture to a large number of foreign visitors and media," said Tjaco Walvis, a branding expert who researched the impact of previous expos. "It helps to put the organizing city on the mental world map."
Sometimes, though, the mark it leaves can turn into a stain. One expo was forced to declare bankruptcy during its run. The 1984 Louisiana World Exposition in New Orleans suffered from low attendance and funding problems. It managed to stay open until its closing day only after the U.S. government provided financial support.
And while expo officials point to urban development as a major benefit of hosting, it comes at a cost. In the preparations for the Shanghai World Expo, the Chinese authorities demolished tens of thousands of homes and displaced a total of 18,000 families, according to Amnesty International, a human rights group.
Some also argue that the megabillions paid to host an expo could be better spent and create more direct benefits for the city.
"Hosting an expo on its own will do little long term," said Andrew Scott, deputy dean of the London Business School, adding that only as part of a larger economic program could hosting be successful.
Still, if an expo proves a success, the organizers can count on media coverage and international tourism as a boost to the host's image at home and abroad. But it is not just the host city that benefits from the exposure.
"Participating countries can use the event to strengthen their national 'brands' by developing impactful and memorable pavilions," Mr. Walvis said. The Dutch pavilion at Expo 2000 in Hanover, Germany, generated about €350 million, or $468 million, in indirect long-term economic benefits for the Netherlands, more than 10 times the investment, Mr. Walvis's research shows.
It is understandable, then, why more and more international cities find the prospect of hosting or participating in an expo appealing. But for visitors, too, an expo can be an exciting event.
"World expositions play to the fascination of the unknown and the charm of other cultures and countries," Mr. Walvis said. "They allow people to travel around the world in just a day."
This article originally appeared in The New York Times.