NEW YORK, NY - NOVEMBER 07: The Empire State Building rises above Midtown Manhattan on November 7, 2016 in New York City. The city is on a hightened state of alert after federal authorities warned of a possible terrorist attack before the U.S. election. Both Democratic presidential nominee Hillary Clinton and Republican nominee Donald Trump plan to spend election night in New York City. John Moore/Getty Images/AFP== FOR NEWSPAPERS, INTERNET, TELCOS & TELEVISION USE ONLY ==
These five smart cities epitomise sustainability and efficiency.
Barcelona, Spain
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