Geographic research works. Based on historical and geographical special books such as "Historical Records" to "Ming Dynasty Records", this book conducts detailed research on many historical and geographical conditions from Beijing to Shanhaiguan. It includes a test of Ji, a supplementary annotation of Eryan Zhuan in "Hanshu", an analysis of Shimen, an analysis of the errors of Yang Ling Temple in "Yi Tong Zhi", and an analysis of Liucheng. There are twenty-three chapters, including Examination of Changli, Distinguishing Three Hans, and Examination of the Great Wall, totaling more than 11,000 words.
