Pei Xiu (224–271), courtesy name Jiyan, was a Chinese cartographer, geographer, politician, and writer of the state of Cao Wei during the late Three Kingdoms period and Jin dynasty of China. He was very much trusted by Sima Zhao, and participated in the suppression of Zhuge Dan's rebellion. Following Sima Yan taking the throne of the newly established Jin dynasty, he and Jia Chong had Cao Huan deprived of his position to accord to the will of heaven. In the year 267, Pei Xiu was appointed as the Minister of Works in the Jin government. Pei Xiu outlined and analysed the advancements of cartography, surveying and mathematics up until his time. He criticised earlier Han dynasty maps for their lack of precision and quality when representing scale and measured distances, although 20th century archaeological excavations and findings of maps predating the third century prove otherwise. There is also evidence that Zhang Heng (78–139) was the first to establish the grid reference system in Chinese cartography. As a cartographer Pei Xiu is best known for his work in cartography. Although professional map-making and use of the grid had existed in China before him, he was the first to mention a plotted geometrical grid reference and graduated scale displayed on the surface of maps to gain greater accuracy in the estimated distance between different locations. Historian Howard Nelson asserts that there is ample written evidence that Pei Xiu derived the idea of the grid reference from the map of Zhang Heng (78–139 CE), a polymath inventor and statesman of the Eastern Han period. Robert Temple asserts that Zhang Heng should also be credited as the first to establish the mathematical grid in cartography, as evidenced by his work in maps, the titles of his lost books, and the hint given in the Book of Later Han (i.e. Zhang Heng "cast a network of coordinates about heaven and earth, and reckoned on the basis of it"). Xiu also created a set of large-area maps that were drawn to scale. He produced a set of principles that stressed the importance of consistent scaling, directional measurements, and adjustments in land measurements in the terrain that was being mapped. The preface to Pei Xiu's written work was preserved in the 35th volume of the Book of Jin, which is the official history for the Jin dynasty and one of the Twenty-four Histories. It was written in