![]() This method is very accurate but slow and tedious. ![]() It is a method in which reasonable cost is required. If that benchmark is not present a temporary benchmark is considered.įig: Contour lines drawn by tachometric method of contouring Comparison between Direct and Indirect methods of contouring: Direct Method In finding the vertical control points the leveling instruments are used and all these points are according to a benchmark of known reduce level. This is an accurate method but time-consuming method. In this method, the contour lines are traced and marked on the ground by locating the horizontal controls and vertical controls of the points which lie on these contour lines. These elevations can be found out by following two methods: Methods used in locating the contour lines:Ĭontour lines can only be drawn if the elevations of selected points are known both horizontally and vertically. After drawing the four contour lines the fifth line should be thicker than other lines so that it is easy to read.When the length of the contour line is very long then elevation should be written at more than one place.Each elevation should be mentioned corresponding to each contour line.Drawing pen should be used while drawing the contour lines and should be black or dark brown in color for perfect visibility.French curves can also be used to draw smooth curves.When the contour points are located then contour lines are drawn that connects those points by smooth and free hand curves.When contour lines are very close and higher values inside show a hill or peak.įig: Contour lines showing a valley Drawing of contour line:.A coastline is a zero-meter contour line.Contours have soft and smooth turns and are not very sharp.Contour lines never pass-through permanent structures.Irregular contour lines are the indication of an uneven surface.Equally spaced contour lines are the indication of a uniform slope.Closely spaced contour lines are the indication of steep ground.The elevations of the contour lines are written or shown adjacent to the contour.Widely spaced contour lines are the indication of a flat surface.Ridge and contour lines always cross each other at the angle of 90 degrees means at the right angle.Any two contours of different elevations never intersect or cross each other except in the case of an overhang cliff or a cave.It can be represented by tanθ.Ĭontour gradient is shown in a format of 1 in S, here 1 is the vertical component and S is the horizontal component of a slope and both have the same units. It is a line that maintains a constant slope throughout the horizontal ground surface. Contour Gradient:Ī contour gradient is a line that shows the slope of the ground surface or terrain between two successive contour lines and can be ascending or descending. For example: If the ground is steeper, the horizontal equivalent will be less. The steepness of the ground is the main factor that has a great effect on the value of horizontal equivalent. The horizontal equivalent is a value that varies from point to point and is not constant. ![]() The horizontal distance between two successive contours is known as the horizontal equivalent. The contour interval and scale of the map are inversely proportional to each other. The purpose for which it is to be uses, time, and the type and nature of the surface of the ground. The Contour interval should be a constant value. ![]() The contour interval is dependent on many factors such as the scale of the contour map. ![]() The distance between two successive contours vertically is known as contour interval. ![]()
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