![]() ![]() U-shaped contour lines with convexity 2V-shaped contour lines with convexity. Ridge is indicated by contour lines with a U-shape and convexity towards the lower land. Hills are shown by approximately circular closed contours with rising values towards the centre. A pond is shown by approximately concentric closed contours with diminishing values towards the centre. Uneven surfaces are indicated by irregular outlines. A consistent slope is indicated by an evenly spaced contour. The close spacing of the contours implies that the land is steep. A flat surface is shown by a contour that is widely separated. The following are the properties of contour maps:Contour lines must close, but not necessarily within the plan’s boundaries. The contour lines in a given area are drawn with the difference in elevation between them in mind. After defining lowered levels of numerous points in the area, such lines are drawn on the plan of the area. Contour Maps and Their Applications Contour lines are imaginary lines that connect places of equal elevation on a contour map. If the map is particularly large, it is also written at the ends. Every contour line has its elevation indicated on it. Every fifth contour line has been thickened to make it easier to read. A surveyor should not lose sight of the ground’s distinguishing feature. Smooth lines can be drawn using French curves. Smooth contour lines are generated after identifying contour points and linking corresponding points on a contour line. Similarly, the contour points of any line connecting two places may be different. The points on the 98 m and 99 m contours are represented by the intersection of dark lines on AB. Rotate the tracing sheet so that point B is intersected by the parallel line 100.2. Then, on A, keep the second parallel line in place. If A’s RL is 97.4 and B’s is 99.2 m, then Assume that the bottom darkest line represents 97 m RL and that each parallel line is spaced at 0.2 m intervals. To make counting easier, every tenth or fifth line is darkened. The mechanical or graphical method of interpolation involves utilising a tracing sheet to linearly interpolate contour points: Several parallel lines are drawn at regular intervals on a tracing sheet. The cross-section spacing is determined by the type of the terrain, the map’s size, and the contour interval necessary. On the drawing sheets, the points are marked, their reduced levels (RL) are noted, and contour lines are interpolated. All of those points are established by levelling the reduced level. Cross-Section Methodology This method involves taking cross-sectional points at regular intervals. Interpolation is used to draw contour lines and reduced levels of grid points. After that, a grid square is drawn on the drawing sheet. Levels of all grid points are established through levelling. The standard square dimension ranges from 5 m x 5 m to 20 m x 20 m. As a result, horizontal control is used in this strategy. Contouring by Indirect Method Levels are taken at a few specified spots and their levels are decreased using this procedure. This procedure is time-consuming and tedious, but it is accurate. Hand levels and Abney levels are sometimes utilised to speed up the levelling process. It is preferable if both are in close proximity so that they can communicate easily. It is not necessary to change the level and survey instrument at the same time. The instrument is relocated to another point to cover greater area when the appropriate points are established from the instrument setting. For this project, a plane table survey is perfect. It is adhered to.Īs a result, multiple points are established on one or two contour lines and appropriately noted down. After that, the instrument man guides the staff man to another location where he can find the identical staff reading. Using his instruments, a surveyor establishes horizontal control of that location. The instrument operator instructs the staff operator to roam about the area until the required staff reading is found. The collimation plane/instrument height is determined, and the needed staff reading for a contour line is calculated. After taking fly levels from a nearby bench mark, a level is set on a commanding location in the region. A levelling instrument is widely used for vertical control. It entails determining the vertical and horizontal controls of the points on the chosen contour line.
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