《论衡·卷十一·谈天篇》
东海与沙漠，是中国东、西的边沿，相隔万里，看北斗星还是在北面，这是因为地方狭小，不能远离北斗星的缘故。
东海、流沙，九州东西之际也，相去万里，视极犹在北者，地小居狭，未能辟离极也。
The East China Sea and the desert are the eastern and western borders of China. Although thousands of miles apart, the Big Dipper is still in the north when observed. This is because the area is small and cannot be far away from the Big Dipper.