The form of the ground
A steep slope is one with a large angle between the sur face and the horizontal, and a gentle slope is one with a small angle. An even slope is one where the angle is constant, and an uneven slope is one where the angle changes. A level piece of ground is one which has the same elevation at all places. A flat piece of ground is not necessarily level, the surface of a board for instance is flat in any position. The terms valley, ridge, gulley, etc., are well enough known so description here may be omitted.There are two methods used on maps for showing the form of the ground. The most common is the Contour method, and the other, now very seldom used except on very small scale maps, is the Hachure method.
Contours should be thought of as lines cut Contours from the earth by a series of imaginary level
surfaces, with equal vertical distances be tween them. The French call them "courbes horizontales reprcsentant le terrain." The vertical distance between the imaginary surfaces is called the "Contour Interval" or some times the "Vertical Interval." (Abbreviated Contour C. I. or V. I.) Since a contour is a line in a Interval level surface, all points on it are of the same elevation or contours are lines joining points of the same elevation.
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