▁the ▁history ▁of ▁map making ." ▁ ▁Gem ma ▁F ris ius ▁was ▁the ▁first ▁to ▁propose ▁the ▁use ▁of ▁a ▁chron ometer ▁to ▁determine ▁longitude ▁in ▁ 1 5 3 0 . ▁In ▁his ▁book ▁On ▁the ▁Princi ples ▁of ▁Astronom y ▁and ▁Cos m ography ▁( 1 5 3 0 ), ▁F ris ius ▁explains ▁for ▁the ▁first ▁time ▁how ▁to ▁use ▁a ▁very ▁accurate ▁clock ▁to ▁determine ▁longitude . ▁The ▁problem ▁was ▁that ▁in ▁F ris ius ' ▁day , ▁no ▁clock ▁was ▁sufficiently ▁precise ▁to ▁use ▁his ▁method . ▁In ▁ 1 7 6 1 , ▁the ▁British ▁clock - builder ▁John ▁Harrison ▁constructed ▁the ▁first ▁marine ▁chron ometer , ▁which ▁allowed ▁the ▁method ▁developed ▁by ▁F ris ius . ▁Tri ang ulation ▁had ▁first ▁emer ged ▁as ▁an ▁efficient ▁method ▁in ▁cart ography ▁( map making ) ▁in ▁the ▁mid ▁six teenth ▁century ▁when ▁F ris ius ▁set ▁out ▁the ▁idea ▁in ▁his ▁Lib ell us ▁de ▁loc orum ▁descri b endor um ▁r ation e ▁( Book let ▁concerning ▁a ▁way ▁of ▁describing ▁places ). ▁Dutch ▁scient ists ▁Jacob ▁van ▁De vent er ▁and ▁Wille br ord ▁S nell ▁were ▁among ▁the ▁first s ▁to ▁make ▁system atic ▁use ▁of ▁tri ang ulation ▁in ▁modern ▁surve ying , ▁the ▁technique ▁whose ▁theory ▁was ▁described ▁by ▁F ris ius ▁in ▁his ▁ 1 5 3 3 ▁book . ▁Ger ard us ▁Mer c ator ▁is ▁considered ▁as ▁one ▁of ▁the ▁found ers ▁of ▁modern ▁cart ography ▁with ▁his