《梦溪笔谈·辨证二》
渡过长江而后至于云泽，进入云泽然后至于郧地，那么云泽必定是在长江以北。
涉江而后至云，入云然后至郡，则云在江北也。
After crossing the Yangtze River and then arriving at Yunze, and then entering Yunze and then arriving at Yun, then Yunze must be north of the Yangtze River.