Comprehensive Geography Study Guide: Contour Lines and Slopes
Definition and Fundamental Nature of Contour Lines
Contour lines, known as kontoerlyne in Afrikaans, are essential cartographic tools used to represent the three-dimensional shape of the earth's surface on a two-dimensional map. They are specifically defined as lines on a map that connect various geographical points that share the exact same height or altitude above sea level. By tracing these lines, a map user can visualize terrain features such as hills, valleys, and plains without requiring a physical 3D model.
Universal Rules and Characteristics of Contour Lines
To ensure accuracy and readability in geographical surveys and examinations, such as the SW-GEO KW2, there are several strict rules regarding the behavior of contour lines. First, contour lines never cross one another. Because a single point on the ground cannot have two different altitudes simultaneously (unless there is a rare overhanging cliff), the lines on a map must remain distinct. Second, contour lines never split or divide. They must either form a continuous closed loop within the map or extend to the edges of the map sheet without bifurcating.
The Relationship Between Contour Spacing and Terrain Slope
The distance between contour lines on a map is the primary indicator of the gradient or steepness of the terrain. When contour lines are drawn very close to each other, it indicates a steep slope (steil helling). This is because the elevation is changing rapidly over a very short horizontal distance. Conversely, when contour lines are positioned far away from each other, it represents a gradual or gentle slope (geleidelik helling), indicating that the terrain rises or falls slowly over a long distance. In cases where the contour lines are spaced evenly or at regular intervals from one another, the terrain is characterized as having a uniform or even slope (eenvormig helling), where the angle of the incline remains constant.
Understanding Vertical and Contour Intervals
A critical concept in map reading is the Vertical Interval (), also frequently referred to as the Contour Interval. This is defined as the exact difference in height between two consecutive contour lines. For example, if one line is marked at and the next is marked at , the vertical interval for that map is . This interval is generally consistent throughout a single map to allow for standardized measurement and comparison of different topographical features.
Specific Topographic Formations: Concave and Convex Slopes
Topography can be further categorized by the specific arrangement of contour lines, which illustrates the curvature of a hillside. A concave slope (konkawe helling) is identified by a specific pattern where the contour lines are placed very close together at the higher elevations near the top of the hill but become increasingly spread out toward the bottom or the base. This indicates a slope that is steep at the top and levels out as it reaches lower ground.
In contrast, a convex slope (konvekse helling) exhibits the opposite pattern. On a convex slope, the contour lines are spread far apart at the top of the hill, signifying a gentle start to the descent. However, as the elevation decreases, the contour lines become much closer together toward the bottom. This indicates that the slope starts gradually but becomes increasingly steep as one moves down the hill. Understanding these patterns is vital for identifying terrain types and landforms appearing in numerical data sets ranging from values like , , and up to .