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. 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.
explanation:
![What do lines on a contour map indicate?](/tpl/images/04/02/vIjfqWkzkA47vTxR.jpg)