Question

Which of the following is not the characteristic of contours?

• A. The contour lines of different elevations cannot cross each other
• B. The contour lines of different elevations can unite to form one line only in the case of a vertical cliff
• C. The contour lines close together indicate steep slope
• D. The contour lines cross a valley at right angles but they do not cross a watershed line at right angle

Hint:

Understanding contour characteristics is crucial for interpreting topographic maps. Remember that contours never cross (except for overhanging features), closely spaced contours indicate steep slopes, and contours form V-shapes pointing upstream in valleys and V/U-shapes pointing downstream along ridges, always crossing these lines at right angles.

Answer 1

The Correct Option is D

Step 1: Understand the characteristics of contour lines.
Contour lines are imaginary lines on a map that connect points of equal elevation. They are fundamental in representing the topography of an area. Their characteristics are derived from the geometric properties of the terrain they represent.
Step 2: Evaluate each given characteristic.

• (1) The contour lines of different elevations cannot cross each other: This is a fundamental characteristic of contours. If contour lines of different elevations crossed, it would imply that a single point on the ground has two different elevations simultaneously, which is impossible in nature. The only exception is an overhanging cliff or cave, where contours *can* appear to cross on a 2D map, but in 3D space, they are at different levels. However, for typical topographical features, they do not cross. This statement is generally true.
• (2) The contour lines of different elevations can unite to form one line only in the case of a vertical cliff: This is also a true characteristic. When a surface is perfectly vertical (like a vertical cliff), multiple contour lines of different elevations will coincide and appear as a single line on the map because they all pass through the same horizontal position at different vertical heights. This statement is true.
• (3) The contour lines close together indicate steep slope: This is true. Where contour lines are drawn closer together, it signifies a rapid change in elevation over a short horizontal distance, indicating a steep slope. Conversely, widely spaced contour lines indicate a gentle slope. This statement is true.
• (4) The contour lines cross a valley at right angles but they do not cross a watershed line at right angle: This statement contains an inaccuracy.
  • Valleys: Contour lines cross valleys (or streams) at right angles (or approximately right angles) and typically form V-shapes pointing upstream (towards higher elevation). This part is true.
  • Watershed (Ridge) Lines: A watershed line (also known as a ridge line or divide) is a line separating two drainage basins. Contour lines also cross watershed (ridge) lines at right angles (or approximately right angles). In this case, the V-shape or U-shape of the contour lines points towards lower elevation. The statement claims they *do not* cross a watershed line at a right angle, which is false.

Step 3: Identify the incorrect characteristic.
The characteristic stated in option (4) regarding watershed lines is incorrect. Contour lines cross both valleys and ridges (watershed lines) approximately at right angles. $$\boxed{\text{The contour lines cross a valley at right angles but they do not cross a watershed line at right angle}}$$