从高空俯瞰中国大地，地势像四级阶梯，自西向东，逐级下降。
A bird's-eye view of China would indicate that China's terrain descends in four steps from west to east.
浅滩泥沙输移方向自西向东。
但是由于地球自西向东的旋转，所以这种方法并不适合于经度的计算。
But since the earth spins always eastward that trick doesn’t work with longitude.
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