Map Contour Lines: Purpose and Drawing

Contour lines are lines drawn on a map connecting points that share the same elevation above a reference point, typically sea level. These lines are crucial tools in cartography for illustrating the shape and topography of the land. By observing how contour lines are spaced and shaped, one can easily understand the terrain's features, such as hills, valleys, and slopes.

Understanding Contour Intervals

The contour interval signifies the vertical distance in elevation between any two adjacent contour lines. To ensure clarity and consistency on maps, contour lines are usually plotted at fixed intervals. The choice of this interval is influenced by several factors:

• Map Scale: Larger scale maps (showing smaller areas in greater detail) typically use smaller contour intervals, while smaller scale maps (covering larger areas) use larger intervals.
• Terrain Characteristics: Steep terrains necessitate smaller intervals to depict the rapid changes in elevation effectively, whereas gentle terrains might use larger intervals without losing significant detail.

Consistent spacing of contour lines directly indicates the steepness of the slope: closely spaced lines denote steep areas, while widely spaced lines indicate gentle slopes.

Common Contour Interval Heights on Maps

To maintain uniformity in mapmaking, specific sets of contour intervals are commonly adopted. Let's examine the provided options in the context of standard practices:

• Option 1: Provides intervals of 100 metres, 200 metres, and 300 metres. These are generally large intervals, suitable for small-scale maps covering extensive regions.
• Option 2: Offers intervals of 50 metres, 200 metres, and 500 metres. This combination includes very large intervals (200m, 500m) that might be too coarse for detailed topographical representation.
• Option 3: Presents intervals of 20 metres, 50 metres, and 100 metres. These values offer a good balance, suitable for various map scales and providing adequate detail for most general and specialised topographical maps. They are widely used in modern map reading and surveying.
• Option 4: Includes intervals of 100 metres, 500 metres, and 1000 metres. These are exceptionally large intervals, typically reserved for very small-scale overview maps, such as continental or world maps.

Considering the need for detail and applicability across different map types, the set representing the typical fixed intervals often includes 20 metres, 50 metres, and 100 metres.