Une ville est un milieu physique où se concentre une forte population humaine, et dont l'espace est aménagé pour faciliter et concentrer ses activités : habitat, commerce, industrie, éducation, politique, culture, etc. Les principes qui régissent la structure et l'organisation de la ville sont étudiés par la sociologie urbaine, l'urbanisme ou encore l'économie urbaine.
L'ONU estime que 2008 est l'année où pour la première fois, de l'histoire connue, plus de la moitié des humains résident dans une ville.
Shanghai is the largest city by population in China and the largest city proper by population in the world. It is one of the four direct-controlled municipalities of China, with a total population of near 24 million as of 2013[update]. It is a global financial center, and a transport hub with the world's busiest container port. Located in the Yangtze River Delta in East China, Shanghai sits at the mouth of the Yangtze River in the middle portion of the Chinese coast. The municipality borders the provinces of Jiangsu and Zhejiang to the north, south and west, and is bounded to the east by the East China Sea.
For centuries a major administrative, shipping, and trading town, Shanghai grew in importance in the 19th century due to European recognition of its favorable port location and economic potential. The city was one of several opened to foreign trade following the British victory over China in the First Opium War and the subsequent 1842 Treaty of Nanking which allowed the establishment of the Shanghai International Settlement. The city then flourished as a center of commerce between east and west, and became the undisputed financial hub of the Asia Pacific in the 1930s. However, with the Communist Party takeover of the mainland in 1949, trade was reoriented to focus on socialist countries, and the city's global influence declined. In the 1990s, the economic reforms introduced by Deng Xiaoping resulted in an intense re-development of the city, aiding the return of finance and foreign investment to the city.