Contours are shown on a map as faint red-brown lines that are specifically drawn to connect points of equal elevation above sea level. These distinctive lines serve as a visual representation of the land's height and shape, providing crucial insights into the terrain.
Understanding Contour Lines
Contour lines are fundamental tools in cartography, offering a two-dimensional depiction of a three-dimensional landscape. As stated in cartographic principles (e.g., documented on 25-Feb-2021), they are defined by their unique properties and purpose:
- Visual Representation: Contours appear as faint red-brown lines meticulously drawn across the map's surface. This specific color and subtlety ensure they are distinguishable yet do not overshadow other map features.
- Elevation Connection: Each contour line connects all points on the map that share the exact same elevation above a specific datum, typically mean sea level. This means if you were to physically walk along a contour line on the actual terrain, your elevation (height of the land) would remain constant.
- Terrain Insight: Beyond just showing elevation, contour lines collectively illustrate the shape of the terrain. Their spacing, pattern, and orientation reveal features like hills, valleys, ridges, and slopes.
Key Aspects of Contour Line Representation
To effectively show contours, maps adhere to specific conventions:
- Index Contours: Every fifth contour line is usually bolder and labeled with its elevation value. These are known as index contours, making it easier to read the map and quickly identify major elevation changes.
- Intermediate Contours: The lines between the index contours are thinner and typically not labeled individually. Their elevation can be determined by counting up or down from the nearest index contour, based on the map's contour interval.
- Supplementary Contours: In very flat areas where the standard contour interval might not show enough detail, dashed or dotted lines called supplementary contours may be used to show additional elevation changes at half the normal interval.
What Contour Lines Reveal
The way contour lines are drawn provides a wealth of information about the topography:
- Slope Steepness:
- Closely spaced contour lines indicate a steep slope, where the elevation changes rapidly over a short horizontal distance.
- Widely spaced contour lines suggest a gentle slope or relatively flat terrain.
- Terrain Features:
- Concentric circles often represent hills or mountains, with the smallest circle indicating the summit.
- V-shaped contours usually point upstream when crossing a river or stream, indicating a valley.
- U-shaped contours generally point downhill, indicating a ridge.
Summary of Contour Line Characteristics
| Characteristic | Description |
|---|---|
| Appearance | Faint red-brown lines drawn on the map. |
| Purpose | Connect points of equal elevation above sea level. Show elevation and the shape of the terrain. |
| Implication | If physically followed, the elevation (height of the land) would remain the same. |
| Interpretation | Spacing indicates slope steepness (close = steep, wide = gentle). Patterns reveal landforms (concentric circles for hills, V-shapes for valleys). |
By understanding how these faint red-brown lines are presented and interpreted, map users can accurately visualize the land's three-dimensional characteristics from a two-dimensional map.
