lined ▁six ▁principles ▁that ▁should ▁be ▁observed ▁when ▁creating ▁maps , ▁two ▁of ▁which ▁included ▁the ▁rect angular ▁grid ▁and ▁the ▁graduated ▁scale ▁for ▁meas uring ▁distance . ▁Western ▁histor ians ▁compare ▁him ▁to ▁the ▁Greek ▁P to le my ▁for ▁his ▁contributions ▁in ▁cart ography . ▁However , ▁Howard ▁Nelson ▁states ▁that , ▁although ▁the ▁accounts ▁of ▁earlier ▁cart ographic ▁works ▁by ▁the ▁invent or ▁and ▁official ▁Z hang ▁H eng ▁( 7 8 – 1 3 9 ) ▁are ▁somewhat ▁vague ▁and ▁sketch y , ▁there ▁is ▁am ple ▁written ▁evidence ▁that ▁Pe i ▁X iu ▁derived ▁the ▁use ▁of ▁the ▁rect angular ▁grid ▁reference ▁from ▁the ▁maps ▁of ▁Z hang ▁H eng . ▁ ▁Later ▁Chinese ▁ideas ▁about ▁the ▁quality ▁of ▁maps ▁made ▁during ▁the ▁Han ▁D ynast y ▁and ▁before ▁stem ▁from ▁the ▁assess ment ▁given ▁by ▁Pe i ▁X iu . ▁Pe i ▁X iu ▁noted ▁that ▁the ▁ext ant ▁Han ▁maps ▁at ▁his ▁dispos al ▁were ▁of ▁little ▁use ▁since ▁they ▁featured ▁too ▁many ▁in acc ura cies ▁and ▁ex agger ations ▁in ▁measured ▁distance ▁between ▁locations . ▁However , ▁the ▁Q in ▁State ▁maps ▁and ▁M aw ang du i ▁maps ▁of ▁the ▁Han ▁era ▁were ▁far ▁superior ▁in ▁quality ▁than ▁those ▁exam ined ▁by ▁Pe i ▁X iu . ▁It ▁was ▁not ▁until ▁the ▁ 2 0 th ▁century ▁that ▁Pe i ▁X iu ' s ▁ 3 rd - century ▁assess ment ▁of ▁earlier ▁maps ' ▁dis mal ▁quality ▁would ▁be ▁over turn ed