Index contour lines are the darker, thicker lines found on topographic maps that indicate specific elevations. They are typically spaced at regular intervals, such as every 100 or 500 feet, depending on the map’s scale and the terrain’s relief.
These lines serve as reference points, providing a quick way for map readers to understand the elevation changes in a particular area. Between index contour lines, additional lighter contour lines show the gradual changes in elevation. By interpreting these lines, outdoor enthusiasts can better gauge the steepness of hills, valleys, and other features of the landscape.
In summary, index contour lines are essential elements of topographic maps, aiding in navigation and enhancing our understanding of the topography of an area.