The postcode of Xuanwu District is 2 100 18. According to the postal code database, the postal code consists of Arabic numerals, and the postal code of Xuanwu District is 2 100 18. Xuanwu District is located in the middle of Nanjing, Jiangsu Province. It is one of the eight districts in the main city of Nanjing, an important scientific research, culture and business center in China, and a modern service industry base in East China. It is the seat of the Nanjing Municipal Party Committee, the municipal government and many provincial and municipal organs, and also the seat of the military leaders of the Eastern Theater and the Eastern Theater Air Force. Xuanwu District has 9 universities including Southeast University, Nanjing University of Science and Technology, Nanjing Forestry University and Nanjing Agricultural University, and 22 research institutes including Nanjing Branch of Chinese Academy of Sciences and Jiangsu Academy of Agricultural Sciences. One-third of the academicians of the two academies in Jiangsu Province and about half of the key laboratories at or above the provincial level in Nanjing are located in China. Nanjing Museum, one of the three major museums in China, and Nanjing Library, the fourth largest library in Asia, is known as Purple Mountain Observatory of Chinese Academy of Sciences, the cradle of modern astronomy in China.