Which of the following describes the concept of contour lines?

Contour lines are defined as lines on a map that connect points of equal elevation above a given level, typically sea level. These lines provide a visual representation of the terrain's shape and slope. When contour lines are close together, they indicate a steep gradient, while wider spacing denotes gentler slopes. By analyzing the arrangement of contour lines, one can understand the topography of the landscape, including hills, valleys, and flat areas.

The other options do not accurately describe contour lines. Paths taken by rivers relate to waterways, not elevation. Human boundaries pertain to jurisdictional or political lines, lacking any reference to elevation. Transportation routes represent pathways for travel and transport, which do not convey information about elevation or landform shapes. This distinction reinforces the specific role of contour lines in map interpretation and physical geography.