LONDON -- Close your eyes and imagine the possible scenarios in 2016.
Olympic athletes strolling to competition venues along Chicago's lakefront. Volleyball players diving on the sand of Rio de Janeiro's Copacabana beach. Cyclists whizzing past Tokyo's Imperial Palace. Soccer players curling free kicks in Madrid's Bernabeu stadium.
After a two-year global campaign featuring four world-class cities, one of the closest bid races in Olympic history will be decided next Friday in a vote of the International Olympic Committee in Copenhagen.
Although IOC votes -- by secret ballot over several rounds -- can be highly unpredictable, Rio and Chicago look to be the main contenders.
At stake is international prestige, billions of dollars in potential investment and economic spinoffs, and the honor of staging the world's biggest sports extravaganza.
The decision may come down to two key issues: Will President Barack Obama go to Copenhagen to pitch Chicago's case in person? Is the IOC ready to take a bit of a gamble on Rio and send the Olympics to South America for the first time?
"I expect a vote difference of a couple of votes only," IOC president Jacques Rogge told The Associated Press in a recent interview. "There is no favorite. There is no bid that is lagging behind. All the scenarios are possible."
Technical issues, emotion, sentiment, geography, politics, self-interest and other intangibles all play a role in IOC votes.
In this race, Rio -- besides its iconic beaches and stunning backdrop -- has the strongest emotional pull of the four candidates: The Olympics have never been held in South America and the time has come to try something new.
"For others it would be just another Olympics, but for Brazil it would be something to raise the self esteem of the people," Brazilian President Luiz Inacio Lula da Silva said this week. "No other city needs to host an Olympics. Brazil needs it. ... Do only rich countries have the right to host the Olympics?"
With Africa the only other continent that hasn't staged an Olympics, Rio's argument has resonated with many IOC members who espouse the "universality" of the games and like to make a geopolitical statement by taking the event to new territories.
"There is sympathy of course for Rio because the games have never been in South America," IOC executive board member Denis Oswald said. "In principle, yes, it would be nice for the universality of the games that we go to a new continent that has never organized games, but only if we are confident that all the technical and other requirements are met."
Rio has bid before, but failed to make the list of finalists for the 2004 and 2012 Olympics. Another South American city -- Buenos Aires, Argentina -- fell short in the vote for 2004, as did a bid from Cape Town, South Africa.
But this time, Rio has made a convincing case for taking the Olympics to a new frontier.
"I'd say for the first time, it's a realistic choice," senior Canadian IOC member Dick Pound said. "We had Cape Town and we've had Brazil and Buenos Aires before. They were there as sort of signals that someday it would be possible. Now you have a real choice. Whether they're prepared to do it is another question.
"You try to pick the least risky place recognizing that they all have some element of risk," he said.
Chicago is bidding to bring the Summer Games back to the U.S. for the first time since Atlanta in 1996. The bid, which would bring the games back to the Olympics' most lucrative market for sponsorships and television rights, is centered on a compact plan putting most athletes within 15 minutes of their venues along picturesque Lake Michigan.
Chicago's hopes could ultimately depend on whether Obama goes to Copenhagen for the vote. Tony Blair, then Britain's prime minister, was instrumental in London's victory when he traveled to Singapore in 2005; and Vladimir Putin helped Sochi get the 2014 Winter Games when he went to Guatemala City in 2007.
Silva and King Juan Carlos of Spain and Spanish Prime Minister Jose Luis Rodriguez will be in Copenhagen. Tokyo is urging new Japanese Prime Minister Yukio Hatoyama to attend, though he hasn't decided yet.
Obama -- who calls Chicago home -- contacted Rogge on Sept. 11 to inform him he wouldn't be traveling to Denmark because of his commitment to reforming American health care, and was sending first lady Michelle Obama and senior White House adviser Valerie Jarrett.
However, the White House sent an advance team to Copenhagen this week to make preparations in case the president decides to join his wife at the last minute -- possibly arriving and departing on the day of the vote.
"If he can be persuaded to go, I think it makes a huge difference," Pound said. "He's a transformational figure in the world today."
Obama has sent a letter to IOC members saying the Olympics would be an "extraordinary opportunity for America to renew our bonds of friendship and welcome the world to our shores with open arms."
Chicago overcame one of its biggest hurdles when the city council approved all financial guarantees for the games, clearing the way for Mayor Richard M. Daley to sign the host city contract if Chicago wins. That was a major step for a U.S. bid city, which -- unlike rival candidates -- can't rely on federal government financial backing.
Yet the Chicago bid could still be affected by lingering anti-U.S. sentiment in the European-dominated IOC and resentment over contentious issues with the U.S. Olympic Committee, including the American body's share of Olympic revenues and plans -- now on hold -- for its own Olympic television network.
British bookmakers list Chicago as an odds-on favorite, followed by Rio, Tokyo and Madrid.
But Rio seemed to pick up the unofficial front-runner's tag in June when the bid cities made presentations to IOC members in a specially arranged meeting in Lausanne, Switzerland. Rio officials made a splash by unveiling a big world map with dots showing where all the Olympics have been held -- and an empty space for South America.
Brazil also claims it is a growing financial power that has been less affected by the global downturn than the other bid countries. It also cites the experience of hosting the 2007 Pan American Games and Brazil's selection as host of the 2014 World Cup, an event which could help prepare infrastructure for the Olympics two years later.
Geography often plays a big role, though the IOC has no official policy of geographical rotation of the games.
Tokyo, which hosted the 1964 Olympics, offers a first-class technical bid and claims it is the safest bet at a time of financial uncertainty and already has $4 billion in the bank for the games. Yet, there is a sense among some IOC members that it would be soon to go back to Asia after last year's stunning Beijing Olympics.
Madrid, which is bidding for a second straight time after a failed attempt for the 2012 Games, also has a strong candidacy with 77 percent of venues already in place. However, it must contend with a reluctance to return to Europe after London in 2012 and Sochi in 2014.
"Although there is no geographical rotation, I think there is a feeling that the games might go west," British IOC member Craig Reedie said. "In which case, you have a choice of two Western Hemisphere cities (Chicago and Rio). The emotional argument is with Rio with regards to the games having never been in South America before."
The result could also hinge on the vagaries of the IOC voting system. Ninety-nine of the IOC's 106 members are eligible to vote in the first round (members from countries with bid cities can't vote while their candidate is still in contention).
The city receiving the fewest votes is eliminated after each round until one candidate secures a majority. The vote is expected to go the maximum three rounds.
Some members tend to vote out of sympathy in the first round, which can produce some surprises. The key to victory is picking up votes from the cities which go out.
If Tokyo were to go out in the first round, it is believed many of its votes would go to Chicago. If Madrid goes out, the consensus is they would go to Rio.
"The real issue for all four cities is to make sure that as far as they can their committed friends vote for them right from round one," Reedie said. "There is danger to all four cities in the first round. After that I'm afraid I have no idea where people might go."
The final 45-minute presentations -- featuring speeches and videos -- also have a role. The consensus is a city doesn't win because of a good presentation, but could lose because of a bad one.
For the first time, there are no IOC executive board meetings in the days leading up to the vote. That means there will be much less opportunity for lobbying and schmoozing. Most IOC members won't be arriving until the day before the vote.
Each city will be bringing celebrity supporters to Copenhagen, including Pele for Brazil and talk show queen Oprah Winfrey for Chicago.
In the end, Rogge said, it will all come down to which bid organizers the members trust most.
"Everything being equal between the four candidates," he said, "I think it's the human factor that will be most important."