LESSON 52

• CLASSIFICATION OF OBTAINING CONTOURS:

  DIRECT METHOD

  INDIRECT METHOD
• METHOD OF OBTAINING CONTOURS:

  TRACE CONTOUR METHOD

  COORDINATE METHOD

  CONTROLLING POINT METHOD

  CROSS PROFILE METHOD

  PHOTOGRAMMETRIC METHOD
• DIRECT METHOD The contours to be plotted are actually traced out in the field. The procedure involves the location and marking of a series of points on each contour line. These points are surveyed and plotted in the field and the appropriate contours are drawn through them.
• INDIRECT METHOD The position and the elevation are not necessarily situated on the contours to be shown, but serve, on being plotted as a basis for the interpolation of the required contours. By indirect method, the points to be located may be either situated along a series of straight lines set over the area or are scattered spot heights at representative points.
• CONTROL POINT METHOD method of obtaining contours is considered to be one with the most universal application. This method is applicable in every type of terrain and condition encountered in topographic mapping.
• CROSS-PROFILE METHOD is principally used in locating contours along a route or other narrow area of terrain. It is a modification of the method of cross sectioning as used in the route surveys.
• BY ESTIMATION Contour lines may be located between points of known elevation by estimation. This method is suitable on small scale maps where the ground form is not too irregular.
• GROUND POINTS are employed as reference in the proper location of the contour lines.
• PHOTOGRAMMETRIC METHOD The availability of aerial photographs and development of photogrammetric methods have expanded rapidly our know-how in the construction of topographic maps.