The term you are looking for is actually known as a ‘contour line’ or ‘isoline.’ These lines are used in various fields such as geography, cartography, and engineering to represent the three-dimensional volume of objects on a two-dimensional plane.
Contour lines connect points of equal value. For instance, on a topographic map, each contour line represents a specific elevation above sea level. This allows us to visualize the terrain and understand the shape and steepness of the landscape.
In a more abstract sense, in fields such as art or design, similar concepts are applied to demonstrate form and volume, helping to convey depth and structure through lines and shapes. Understanding these lines can greatly enhance the interpretation of visual data and help in accurately representing physical phenomena.