What does an index contour line indicate when moving from a lower contour line to an upper contour line?

An index contour line indicates an increase in elevation when moving from a lower contour line to an upper contour line. Contour lines are used on topographic maps to show the shape and elevation of the terrain. Each contour line represents a specific elevation above sea level, and index contour lines, which are typically marked with a number, are usually spaced at regular intervals to indicate significant changes in elevation.

When navigating from a lower contour line to an upper contour line, you are moving upward in elevation, illustrating a rise in the landscape. This concept is fundamental for understanding terrain features and is critical for tasks such as route planning and land navigation in various operations.