Pei Xiu
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.