What's the relationship between contour lines and elevation changes?

Understanding Contour Lines

Contour lines are imaginary lines drawn on a map to show the shape and elevation of the terrain. They connect points of equal elevation, forming a continuous loop around hills, valleys, and other features. By following contour lines, you can visualize the topography of the area and identify features such as ridges, valleys, and plateaus.

Interpreting Contour Intervals

The contour interval is the difference in elevation between adjacent contour lines. This value is typically provided on the map’s legend or key. A common contour interval is 20 feet or 10 meters, but it can vary depending on the map’s scale and intended use. To determine the steepness of the terrain, calculate the vertical distance between two points divided by the horizontal distance between them. This value is known as the slope or gradient. For example, if the contour interval is 20 feet and the horizontal distance between two points is 200 feet, the slope is 1:10. A slope of 1:10 indicates a moderate slope, while a slope of 1:5 indicates a steep slope.

Reading Terrain Features

By combining contour lines and contour intervals, you can identify various terrain features, such as hills, valleys, and ridges. A hill or ridge is typically represented by a series of contour lines that converge or diverge, indicating an increase or decrease in elevation. A valley is often represented by a single contour line that dips below the surrounding terrain. To determine the steepness of the terrain, use the slope formula and compare it to a standard slope chart. This will help you estimate the difficulty of navigating the terrain and make informed decisions about your route.