With more than half of the world population living in cities, one thing is undeniable: we are an urban species. Part game, part urban planning sketching tool, "Cities: Skylines" encourages people to use their creativity and self-expression to rethink the cities of tomorrow. Designer Karoliina Korppoo takes us on a tour through some extraordinary places users have created, from futuristic fantasy cities to remarkably realistic landscapes. What does your dream city look like?