Don't forget to smile when you pass someone in the street today, you never know who could be watching! Australia has been hailed the world's happiest nation and, just to show foreigners why we smile so much, Australia also featured on a list of the world's most liveable cities. The international survey focused on the environment, quality of life and health of more than 30,000 people across the globe. Aussies have the broadest smiles and, apparently, the most liveable cities. The Economist Magazine tipped Melbourne as the second most liveable city in the world, followed by Perth, Adelaide and Sydney which came equal fifth.