There is no specific rule called "rule of V" in topographic map interpretation. However, there are several key concepts related to topographic maps that involve the letter "V" and could be what you are thinking of:

1. "V" Shape of Streams and Valleys:

* Streams and valleys often appear as "V" shapes on topographic maps.

* The point of the "V" points upstream, towards the higher elevation.

* The opening of the "V" points downstream, towards the lower elevation.

2. "V" Shape of Ridges and Spurs:

* Ridges and spurs can also appear as "V" shapes, but the "V" is inverted.

* The point of the "V" points downhill, towards the lower elevation.

* The opening of the "V" points uphill, towards the higher elevation.

3. Contour Lines and Elevation Change:

* Contour lines on topographic maps represent lines of equal elevation.

* When contour lines are close together, it indicates steep terrain.

* When contour lines are far apart, it indicates gentle terrain.

* The "V" shape of streams and valleys is created by the contour lines that represent the elevation change along the valley floor.

To summarize:

* The "V" shape of streams and valleys points upstream.

* The "V" shape of ridges and spurs points downhill.

* The spacing of contour lines indicates the steepness of the terrain.

If you have more details about the "rule of V" you are asking about, please provide them so I can give you a more accurate answer.