由A向B
from A towards B (written)
Structure
由 起点 向 方向／终点 ＋ 动词（流、延伸、发展、推进…）
What it means
Written ‘from A towards B’: 由 marks the starting point (= 从), 向 the direction, and a verb of movement follows.
How it is built
由 + start + 向 + direction + verb (流、移动、延伸), or 由 + A + verb + 向 + B: 冷空气正由北向南移动 (cold air is moving from north to south); 由高处流向低处.
When to use it
Written style; in speech say 从南往北流. 由A到B covers a whole range (由南到北，到处都在下雨) or a change of state (由小到大), not a heading.
Watch out
For something on the move, use 向, not 到: ✗冷空气由北到南移动 ✓冷空气由北向南移动. 由北到南 sweeps across a whole range.
Examples
江水由南向北流去，一路流到北京和天津。
The river water flows from south to north, all the way to Beijing and Tianjin.
冷空气正由北向南移动，明天全省都会降温。
Cold air is moving from north to south, and tomorrow the whole province will turn colder.
这项改革先在几个城市试点，再由点到面、由东向西逐步推开。
The reform was first tried in a few cities, then spread step by step from those points to the whole area, and from east to west.
Learn this in Lesson 172 · HSK 7–9: 南水北调 (Sending southern water north)
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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