Here's how it works:

* Contour lines connect points of equal elevation. Imagine slicing through a landscape with a horizontal plane. Each slice would create a line on the map, representing that specific elevation.

* Spacing: Closer contour lines indicate a steeper slope. Wider spacing means a gentler slope.

* Elevation: Each contour line has an assigned elevation value, usually indicated by a number or a specific interval.

* Index contours: Thicker lines are often used to mark significant elevation changes, making them easier to read.

* Depression contours: These are used to indicate depressions in the terrain. They are represented by hachure marks (short lines perpendicular to the contour line) pointing towards the lower elevation.

Example:

Imagine a hill. If the contour lines are close together at the base of the hill, it indicates a steep ascent. As you move up the hill, the contour lines gradually spread apart, showing a gentler slope.

Understanding contour lines is crucial for interpreting topographical maps and understanding the landscape's shape and features.