This image takes me to a topic in geography: contour, or contour line, or topography.
Topography is the study of the shape and features of the surface of the Earth and other observable astronomical objects including planets, moons, and asteroids. (Wikipedia: Topography).
In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level.(Wikipedia: Contour line)
A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.(Wikipedia: Contour line)
And here you will find an introduction about Contour Maps:
