An imaginary line on which the reduced level is the same at all the points is known as – (RJ ASCO 2011)

✅Explanation:
A contour line is a line on a map that connects points of equal elevation.
-Elevation Representation: Contour lines are a fundamental tool in topographic mapping to represent the three-dimensional shape of the terrain on a two-dimensional map.
-Equal Elevation: All points along a single contour line have the same elevation above a reference datum (usually mean sea level).
-Visualizing Terrain: Contour lines help visualize the shape of the land, including hills, valleys, and slopes.
-Spacing and Steepness: Closely spaced contour lines indicate a steep slope, while widely spaced lines indicate a gentle slope.
-Applications: Contour lines are essential in various fields like surveying, engineering, geology, and environmental science.

🔑Key Points:
Contour Line: It is an imaginary line joining the points of the same elevation above the datum surface.
Contour Surface: An imaginary at which every point is located at the same elevation above the datum is known as contour surface.
Contour Interval: The difference in elevation between successive contour lines on a given map is fixed. This vertical distance between any two contour lines on a map is called the contour interval.
Contour Gradient: An imaginary line on the surface of the earth having a constant inclination with the horizontal (slope) is called contour gradient. It is expressed as the ratio of the vertical height to a specified horizontal distance.
Horizontal Equivalent: The horizontal distance between two points on two consecutive contour lines for a given slope is known as horizontal equivalent. depends upon the slope of the ground and required grade for construction of a road, canal and contour interval.

🛑Additional Information:
(i) Isobars are imaginary lines joining the places having equal values of pressure. The horizontal distribution of pressure is shown by isobars.
(ii) An isohyet or isohyetal line is a line joining points of equal rainfall on a map in a given period. A map with isohyets is called an isohyetal map.