(CNN) World leaders touch down in the Chinese city of Hangzhou this week for the G20 summit and Beijing is determined it will proceed without a hitch. Factories are shuttered, skies are clear and security is tight. Local residents have been given seven days extra vacation time and discounted tours to destinations outside the city to ensure Hangzhou is free of crowds and traffic. Meanwhile, thousands of migrant workers have left the city due to the halt in their work lives and the growing inconvenience caused by G20 preparation measures. What will be discussed at the summit? How has China prepared? And why is it in Hangzhou anyway?