The Yu Chi Thu (Map of the tracks of Yu the great ), the most remarkable cartographic work of its age in any culture , carved in stone in +1137 but probably dating from about +1100 (from Chavannes). The scale of the grid is 100 li to the division. The coastal outline is relatively firm and the precision of the network of river systems extraordinary. The size of the original (which bears the full explanatory text) which is now in the Pei Lin Museum at Sian, is about 3 ft square. The name of the geographer is not known.