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Plotting or reading back any structural element requires determining the declination angles. This can be done digitally using a number of computer drafting programs. However, for this chapter, the exercise will be done by hand for better understanding. The procedure requires first to determine the reference direction (usually north) on the map in question. Next, a protractor is used to measure the angle between the reference direction and the strike or trend line to be measured or drawn (Figure 1.5). Students may need to watch online videos on the use of a protractor if they cannot remember how to use one. Finally, the proper symbol is chosen for drawing or determined for reading back and the angle of dip or plunge is written or read. Dip direction is shown by the tick mark on the side of the strike line and the dip is written next to it. The plunge angle is written on the plunging end of the trend line. Symbols for elements are shown in Table 1.1.

Figure 1.5 Measuring the strike or trend of a structural symbol using a protractor.