RELIEF FEATURES 



The vertical distance between two contour lines is the contour interval. The 

 contour interval may be 10, 50, 100, or any other number of feet. On the 

 maps of the United States Geological Survey, the contours are printed in 

 brown (Plate I). 



The manner in which contours express elevation, form, and grade is shown 

 in the sketch and contour map of Fig. 4. The sketch represents a river 



Fig. 4. Sketch and map of the same area to illustrate the representation 

 of topography by means of contour lines. (U. S. Geol. Surv.) 



valley between two hills. In the foreground is the sea, with a bay which is 

 partly closed by a sand bar. On each side of the valley is a terrace. From 

 the terrace on the right, a hill rises gradually, while from that on the left the 

 ground ascends steeply, in a cliff. Contrasted with this cliff is the gentle 

 descent of the slope at the left. In the map, each of these features is shown 

 by contours directly beneath its position in the sketch. The following expla- 

 nation may make clearer the manner in which contours show elevation, form, 

 and grade: 



