How do index contours let you know if the land you are viewing is increasingor decreasing in elevation?

Index contours are thicker and usually labeled with their elevation. By identifying the index contours on a topographic map, you can determine if the land is increasing or decreasing in elevation. If the index contours are closer together, the land is steep, indicating a rapid change in elevation. Conversely, if the index contours are further apart, the land is gradually increasing or decreasing in elevation.