Huaian is located in the hinterland of northern Jiangsu, bordering Lianyungang and Suqian in the north, Yancheng in the northeast, Yangzhou in the south, Nanjing in Anhui Province in the south and Hongze Lake in the west. With a total area of 10072 square kilometers and a total population of 5,240,600, it now governs 4 counties and 4 districts. Huai' an, with a long history of more than 2,200 years, was once the meeting place of south ships and north horses. It flourished in the Qianlong period of Qing Dynasty, and was called the "Four Metropolis" along the canal with Yangzhou, Suzhou and Hangzhou, enjoying the reputation of "the first male state in Southeast China". The whole city belongs to the Yangtze paraplatform, with Mesoproterozoic as the crystalline basement, well-developed caprock, complex structure, strong depression in Mesozoic and Cenozoic, and the thickness of caprock exceeds 10000 meters.