While drawing a cross-section of a contour map, the following values were noted from point A to point B on a strip of paper to draw the graph - 500 m, 400 m, 300 m, 200 m, 200 m, 300 m, 400 m, 500 m. Which cross-section would be drawn by using the above values?
Understanding Contour Map Cross-Sections
A contour map uses contour lines to represent areas of equal elevation. A cross-section, when drawn along a line on a contour map, shows the shape of the terrain along that specific line. It's like slicing through the landscape and looking at the profile.
Analyzing the Elevation Values for the Cross-Section
The question provides a sequence of elevation values noted along a strip of paper from point A to point B. These values are: 500 m, 400 m, 300 m, 200 m, 200 m, 300 m, 400 m, 500 m.
Let's observe the pattern of these values as we move from point A towards point B:
- Starting at 500 m, the elevation decreases (500 > 400 > 300 > 200).
- It reaches a low point at 200 m and stays at 200 m for a section.
- Then, the elevation increases again (200 < 300 < 400 < 500).
This sequence shows a decline in elevation followed by a rise in elevation, with a low point in between. This pattern is characteristic of a landform feature where the land dips down and then comes back up.
Identifying the Landform from the Cross-Section Pattern
Let's consider the options and how their cross-sections would typically appear based on elevation changes:
- Hill: A cross-section through a hill would show elevation increasing to a peak and then decreasing, or decreasing to a low point (valley) and then increasing towards the hill. The given values show a dip, not a peak.
- Steep slope: A steep slope would show a rapid and continuous change in elevation over a short horizontal distance. The values would consistently increase or decrease, possibly with contour lines close together. The given values show a dip and rise, not just a continuous slope.
- Depression: A depression is a low-lying area surrounded by higher ground. A cross-section through a depression would show elevation decreasing towards the center of the depression (the lowest point) and then increasing as you move away from the center. The given values (decreasing to 200 m and then increasing back to 500 m) perfectly match this pattern, indicating a dip or low point.
- Cliff: A cliff is a very steep rock face, often represented by stacked contour lines or a significant elevation change over a minimal horizontal distance. This would appear as a very rapid drop or rise in elevation in the cross-section. The given values show a more gradual change (100m interval drops/rises), not an abrupt, near-vertical drop like a cliff.
Based on the analysis of the elevation values decreasing to a low point (200m) and then increasing, the cross-section represents a depression.
Visualizing the Cross-Section Shape
If we were to plot these points on a graph with distance on the horizontal axis and elevation on the vertical axis, the line would go down from 500m to 200m, possibly flatten out briefly at 200m, and then go back up to 500m. This shape clearly depicts a hollow or basin-like feature on the land surface.
| Landform | Typical Elevation Pattern in Cross-Section | Match with Given Values (500→200→500)? | |||
|---|---|---|---|---|---|
| Hill | Increase then Decrease (Peak) | No (Shows a dip) | |||
| Steep slope | Continuous Increase or Decrease | No (Shows a dip and rise) | Depression | Decrease then Increase (Low point) | Yes |
| Cliff | Very rapid Decrease or Increase | No (Changes are relatively gradual) |
Therefore, the cross-section drawn using the given values would be that of a depression.
Revision Table: Contour Map Cross-Sections
| Term | Definition/Concept | Relevance to Cross-Sections |
|---|---|---|
| Contour Line | Line connecting points of equal elevation. | Used to determine elevation values for the cross-section profile. |
| Cross-Section | A profile view of the terrain along a specific line. | Shows the vertical shape (hills, valleys, depressions, etc.) of the land. |
| Elevation | Height above a reference point, usually sea level. | The fundamental value represented by contour lines and cross-sections. |
| Gradient/Slope | The steepness of the terrain. Closely spaced contours indicate steep slopes. | Reflected in how quickly elevation changes along the cross-section line. |
Additional Information: Interpreting Contour Maps
Interpreting contour maps involves understanding several key principles:
- Contour Interval: The difference in elevation between consecutive contour lines. This helps determine the vertical scale.
- Contour Spacing: Closely spaced contour lines indicate a steep slope, while widely spaced lines indicate a gentle slope or flat area.
- Closed Loops: Closed contour lines usually represent hills (if values increase inward) or depressions (if values decrease inward, often marked with hachures).
- V-Shapes: Contour lines forming a 'V' shape usually indicate a valley or stream bed. The V points upstream (towards higher elevation).
- Ridges and Spurs: Contour lines curving around a ridge tend to be convex towards lower elevations.
By combining the information from contour lines with the cross-section, you get a complete picture of the terrain's shape.
Important Questions from Contouring
Which of the following statements are CORRECT for contour map?
1) Parallel contour shows uniform slope.
2) Very closed contour shows steep slope.
3) Very closed contour shows flat area.
4) Two contours at different elevation cut at right angle.Identify the correct statements.
i. Contour lines form sharp V-shaped curves across valley line, with the convex side of the curve towards the higher ground.
ii. Contour lines form U-shaped curves across valley line, with the convex side of the curve towards the higher ground.
iii. Contour lines form U-shaped curves across ridge line, with the concave side of the curve towards the higher ground.
iv. Contour lines form sharp U-shaped curves across ridge line, with the convex side of the curve towards the higher ground.
In case of uniform slope, the contour lines:
Contour lines cross a watershed or ridge line at _____ .
The horizontal distance between two consecutive contours is termed as
