Most Populous CitiesSearch for around the world ticketFAQ: How do I use this trip planner?Start by typing your departure city in the box above. Suggestions will appear as you type.Drag and drop destinations to change the order of your trip.Your return city can be the same as your starting city, or you can change it.After adding your cities, click Next to continue planning your trip.Think New York City (#16) or London (#18) have too many people? Try visiting the five most populous cities in the world, in descending order: Shanghai, Mumbai , Buenos Aires, Moscow and Karachi.