The directions and distances described in the Book of the Later Han（後漢書）should be derived from a map created by Pei Xiu （裴秀）, which is not in existence today. However, a short foreword to the map can be seen in the Book of Jin. （晋書）. These data were compared with those from modern maps. The descriptions of the eight directions were half correct, with the rest belonging to adjacent directions. As a result, the length of one “ri” （里） was determined to be 310 meters（mean value of 81 samples with a standard deviation of 45 meters）, a value unprecedented in any documents. This discrepancy may be due to the interpretation of the scale size on Xiu’s map. Additionally, some findings on the distances described in the article about the Wajin（the ancient Chinese name for Japan）in the Annals of the Three Kingdoms （三国志倭人伝） were considered from the perspective of surveying methods.
