依據《左傳》記載，「郭」與「城」位置相臨，「郭」位於「城」之外圍以保護「城」。而依據考古探勘，春秋時代諸國都城，有時「郭」牆完全包圍「城」牆，有時「郭」偏於「城」之一側，有部分「城」牆與「郭」牆相連。由於「城」、「郭」相臨而互為依附，所以《左傳》常將合稱為「城郭」；有時單稱「郭」時亦包括「城」在內，因此形成「城郭」不分的情況。「郛」的位置在「國」與「野」之間，是「國」與「野」的界線。文獻中亦記載，「國」與「野」的分界稱為「封」，可知在空間上「郛」與「封」位置重疊。文獻中常將「封」、「疆」連用，但實則二者有所不同。「郛」與「封」之內稱為「國」、「郊」，「郛」與「封」之外則稱為「野」、「鄙」，而「野」、「鄙」的最外圍是「疆」。「封」作動詞時有冊封土地之意，亦有堆累土石之意；作為名詞則有界線、疆域之意。「封」與「郛」皆是「國」與「野」的界線，而「封」作為挖掘溝塹並堆累土石以為界線，在此意義上「封」可視為「郛」的建築結構。易言之，「郛」的建築有部分即以「封」建構，再配合自然山川形勢減省製作「封」的工事，亦可作為「郛」的天然憑障。「郛」出現早於「郭」，但白春秋時代開始，許多城邑在原本的「城」外再築「郭」以加強防禦。由於「郭」是夯土城牆結構，又較「郛」更具防禦功能，因此世人在較熟悉「郭」的情況下，逐漸與「郛」混同使用，導致「郛」的意義逐漸模糊而被學者遺漏。

The study differentiates between guo and fu in the ”Commentary of Zuo”. According to the Commentary, guo is designed to protect cheng, either surrounding or connecting with it. These two parts are close enough to be inseparable, thus often mentioned as a single word cheng-guo or guo in the Commentary. Fu is the boundary between guo (國) and ye, and in some documents this boundary is recorded as feng. Inside of fu or feng is guo (國) or jiao, outside of fu or feng is ye or bi, and the periphery of ye or bi is jiang. Feng means ”to grant a land” or ”to pile rocks up” when as a verb, and ”boundary” when as a noun. Judging from these definitions and the fact that the locations of feng and fu overlap, feng should be a part of fu constructed partially on natural terrain to save manpower. Guo appears later than fu, but many vassals builds it outside of cheng for defense since the Spring and Autumn Period. Because guo is built with rammed earth and functions better than fu, people are more familiar with guo than fu and gradually confuse them. In consequence, fu gradually has a blurred meaning and becomes misused by scholars.