Contour lines are lines on a map connecting points of equal elevation above or below some datum plane. Without contour lines, maps are not very useful in the study of landforms as they are used on maps to show topography. Characteristics of Contour Lines a. Contour lines may never cross one another (although they may merge-when?). b. Contour lines never split. c. Every contour eventually closes on itself (no dangling!). d. Closely spaced contours indicate a steep slope. e. Widely spaced contours indicate gentle slopes. f. Evenly spaced contours indicate a uniform slope. g. Closed contours indicate hills or ridges (or depressions). h. Depression contours are shown with hachure marks pointing down-slope. i. Contour lines always "V" upstream when crossing a stream or valley. j. Every 5th contour shown on maps is darker and is called an index contour. Note: The exact value of a point lying between two contours cannot be determined exactly; all one can do is determine the range of values within which the point lies. MAP EXERCISE #1: TOPOGRAPHY EXAMPLE (to work through as a class) Draw contours to create a topographic map of the area shown below; label your contours. The numbers give the elevation in feet above sea level of the points marked with an X. Solid lines are streams. Use a contour interval of 100 ft. NOTE: To make it easier, start with the higher elevations, e.g., draw a circle around the 1100+ ft points, then follow down through the 100 ft intervals. 650 630 * 1025 x 1110 950 1025 975 700 x 500 8* 900 710 800 x 890 8. 820 *