Tourism represents 10% of the global economy. But many travel destinations (and the people who live there) are reeling from increasing numbers of tourists, spurred in large part by social media. Correspondent Seth Doane travels to Amsterdam, Paris, Venice and Portofino to look at the impacts that tourism is having on cities, resorts and natural attractions, and why some people are resisting visitors – or redefining tourism – in some of the world’s most popular and fragile destinations.