宋史
The following estimates by different scholars are based upon the number of houses, villages, kokudaka, areas of rice fields and soldiers which were recorded in "" (10th century), "Record of Song or History of Song ()", " (14th century), " (late 16th century), "" (early 17th century), or fragments of papers of the Shōsōin (8th century) and others, as well as remnants of specific periods.