By Mirjam Donath UNITED NATIONS (Reuters) – More than half of the world’s seven billion people live in urban areas, with the top “mega cities” – with more than 10 million inhabitants – being Tokyo, Delhi, Shanghai, Mexico City and Sao Paulo, according to a United Nations report on Thursday. Indeed, urbanization, combined with overall population growth, will boost the number of people in cities by 2.5 billion over the next three decades, with much of that growth in developing countries, especially in Asia and Africa. “Managing urban areas has become one of the most important development challenges of the 21st century,” Wilmoth said. He said providing such services for a dense urban population was typically cheaper and less environmentally damaging than doing the same for a dispersed, rural population.