Answer:

Introduction:
Contour maps are essential tools in civil engineering, geological and topographical surveys to represent the shape and elevation of the land surface. The contour lines on a map provide valuable information about the terrain's steepness, slope, and elevation differences.

Contour Interval:
Contour interval is the vertical distance between two adjacent contour lines on a map. It represents the difference in elevation between the two lines. The contour interval can vary depending on the scale of the map and the terrain's complexity.

Horizontal Distance:
Horizontal distance is the distance between two points measured along a straight line on a horizontal plane. In a contour map, the horizontal distance between two contour lines with the same contour interval represents the slope of the terrain.

Interpretation:
If the horizontal distance between the contour lines having the same contour interval is small, it indicates that the terrain is relatively flat or has a gentle slope. In contrast, if the distance between the contour lines is large, it indicates that the terrain has a steep slope. Therefore, the interpretation of the distance between contour lines depends on the contour interval and the scale of the map.

Plane Surfaces:
If the horizontal distance between the contour lines having the same contour interval is very small, it indicates that the terrain is almost flat or has a plane surface. In this case, the contour lines will be almost parallel, and the area between them will be relatively flat.

Surface with Gentle Slope:
If the horizontal distance between the contour lines having the same contour interval is moderate, it indicates that the terrain has a gentle slope. In this case, the contour lines will be evenly spaced, and the area between them will be gradually sloping.

Surface with Very Steep Slope:
If the horizontal distance between the contour lines having the same contour interval is significant, it indicates that the terrain has a very steep slope. In this case, the contour lines will be closely spaced, and the area between them will be steeply sloping. The closer the contour lines, the steeper the slope.

The Ridge of a Mountain:
The ridge of a mountain is a narrow, elevated strip of land that runs along the crest of a mountain range. If the horizontal distance between the contour lines having the same contour interval is very small and the contour lines are close together, it indicates the ridge of a mountain. The contour lines will be almost parallel and will follow the ridge's shape, representing the elevation changes along the ridge.