Short answers, pulled from the story.
Chongqing is the largest city proper in the world by population because of how its municipality is classified, covering a geographical area roughly the size of Austria. It is the only Chinese city with a resident population of over 30 million, though that figure includes a large rural population. It is not, however, the most populous urban area.
Chongqing means a double celebration, or chongqing in short. The city received the name in 1189 after Prince Zhao Dun of the Southern Song dynasty described his crowning as king and then Emperor Guangzong as a double celebration. To mark his enthronement, Yu Prefecture was converted to Chongqing Fu.
Chongqing served as the provisional wartime capital of the Republic of China during the Second Sino-Japanese War, from November 1937 to May 1946. Chiang Kai-shek retreated there in 1938 after the Battle of Wuhan, and the capital was formally declared on the 6th of September 1940. The city was acclaimed the City of Heroes for its people's endurance under bombing.
Chongqing was separated from Sichuan province and made a direct-administered municipality on the 14th of March 1997 by the Eighth National People's Congress. The resulting entity contained 30,020,000 people across forty-three former counties, and its first official ceremony took place on the 18th of June 1997.
Chongqing is called the Fog City because it has over 100 days of fog per year, with a thick layer enshrouding it for sixty-eight days in spring and fall. It is also one of the Three Furnaces of the Yangtze River, alongside Wuhan and Nanjing, with summer highs of 34 degrees Celsius in July and August.
Chongqing runs the world's longest and busiest monorail system, with 70 stations, and is the only Chinese city to keep public aerial tramways. It is nicknamed the Bridge Capital of China, and its cuisine, part of Sichuan cuisine, is known for spicy, numbing hot pot made with Sichuan pepper.