A contour in geography refers to a line on a contour or topographical map that designates a specific and constant elevation above sea level. Contour lines are used to express a three-dimensional image of terrain on a two-dimensional piece of paper.
Contour lines never cross one another on a topographical map. The proximity of the contour lines to each other also illustrates the steepness of the pictured geographical feature. Lines that are closer to one another suggest a sharp slope, whereas lines that are farther apart designate a more gradual slope. The space between each contour line is called a contour interval. The contour interval always expresses the same distance regardless of how close the contour lines are to one another on a map.