…以南／以北／以东／以西
south / north / east / west of (a line or place), and everything beyond it
Structure
河流／山脉／地名 + 以南／以北／以东／以西 （+ 的 + 地区／土地）
What it means
South (north, east, west) of a line or place, covering the whole area beyond it, not just the strip next to it. 以 is the classical “from”.
How it is built
River, range or place + 以南／以北／以东／以西 (+ 的 + 地区): 长江以南的地区 (the region south of the Yangtze). Once the line is named it can drop: 山岭以南属于中国，以北属于俄国.
When to use it
The standard way to mark out regions in geography, history, treaties and weather forecasts. The spoken X的南边 or X南面 is plainer and often means just south of it.
Watch out
Do not add 边 or 面 (✗ 以南边), and do not use it for people or small objects: ✗ 他坐在我以西 ✓ 他坐在我的左边.
Examples
山岭以南属于中国，以北属于俄国。
The land south of the range went to China, and the land north of it to Russia.
人们常说的“北方”，大致指秦岭—淮河以北的地区。
What people call “the north” is roughly the region north of the Qinling–Huai River line.
这条铁路以东是老城，以西是新开发区。
East of the railway lies the old town; west of it, the new development zone.
Learn this in Lesson 204 · HSK 7–9: 雅克萨与尼布楚 (Albazin and Nerchinsk)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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