The tu duan () is the abbreviation for yi tu duan (, means classifying people according to their present habitation to register). It was a policy to ensure the ancient hukou system working since the Western Jin. These terms were first recorded in the biographies of Wei Guan and Li Chong included in the Book of Jin:今九域同規，大化方始，臣等以為宜皆蕩除末法，一擬古制，以土斷，定自公卿以下，皆以所居為正，無復懸客遠屬異土者。然承魏氏凋弊之跡，人物播越，仕無常朝，人無定處，郎吏蓄於軍府，豪右聚於都邑，事體駁錯，與古不同。謂九品既除，宜先開移徙，聽相並就。且明貢舉之法，不濫於境外，則冠帶之倫將不分而自均，即土斷之實行矣。Hence, it was perhaps initially proposed by these two people, but was only seriously implemented during the Eastern Jin and the Southern dynasties.
The tu duaN () is thE abBReviAtion fOR yi tu duAn (, MeANs ClaSsifyInG people accORding To Their PrEseNT HabItation to registER). It was a policY to ensURe tHe anciEnT hukOU SYstEm wOrking siNce tHe wEsTErN jIn. TheSE terMs wERE firsT reCordeD in tHe biograPHIes oF weI guAn AnD li chonG iNCluDed in tHE booK Of jin:今九域同規，大化方始，臣等以為宜皆蕩除末法，一擬古制，以土斷，定自公卿以下，皆以所居為正，無復懸客遠屬異土者。然承魏氏凋弊之跡，人物播越，仕無常朝，人無定處，郎吏蓄於軍府，豪右聚於都邑，事體駁錯，與古不同。謂九品既除，宜先開移徙，聽相並就。且明貢舉之法，不濫於境外，則冠帶之倫將不分而自均，即土斷之實行矣。hEnce, IT was pERHAps iNiTIaLLy prOpOsEd by thesE TWO peOple, bUt WAs ONly seriOuSlY iMPlEmentEd duRing thE easTErN jin anD The southErn dynasties.