Which of the following scales of the map is not affected due to the shrinking of the map?
📜 Understanding Map Shrinkage
Paper maps are susceptible to changes in their environment. Due to variations in temperature and humidity, the paper or drawing sheet can shrink or expand over time. When the map shrinks, all the distances drawn on it also shrink proportionally.
This creates a problem for numerical scales (like Engineer's Scale or R.F.), because the scale ratio written on the map (e.g., "1:1000") is now incorrect for the shrunken physical drawing.
🔬 Detailed Analysis of the Options
B. Graphical scale
This is the correct answer. A graphical scale (or bar scale) is a line or bar drawn on the map and divided into units of distance (e.g., kilometers or miles). The key advantage is that when the map paper shrinks or expands, the graphical scale shrinks or expands by the exact same proportion. Therefore, the ratio between a distance on the map and the graphical scale remains constant and accurate. Measuring a feature on the shrunken map with the shrunken scale bar will still give the correct ground distance.
A. Engineer's scale & C. Representative fraction
These are incorrect. Both the Engineer's scale (e.g., 1 cm = 50 m) and the Representative Fraction (e.g., 1/5000) are numerical scales. They state a fixed mathematical relationship. If the map shrinks, a physical measurement of 1 cm on the paper no longer represents 50 m on the ground. The numerical scale becomes invalid, leading to measurement errors. You would be using a correct external ruler on an incorrectly sized map.
📊 Summary: Scale Types and Shrinkage
| Scale Type | Format | Effect of Map Shrinkage |
|---|---|---|
| Graphical Scale | A drawn bar with distance markings | Not affected. The scale shrinks with the map, maintaining accuracy. |
| Engineer's Scale | Numerical ratio (e.g., 1 cm = 100 m) | Affected. The stated ratio becomes incorrect. |
| Representative Fraction (R.F.) | Numerical fraction (e.g., 1:10000) | Affected. The stated fraction becomes incorrect. |
💡 Study Tips
- Graphical = Physical: Remember that a graphical scale is a physical drawing on the map. Physical things shrink together.
- Numerical = Abstract: An Engineer's scale or R.F. is an abstract mathematical rule. The rule doesn't change, but the physical map it applies to does, causing a mismatch.
- The Golden Rule: To avoid errors from paper shrinkage, always include a graphical scale on any survey drawing or map.