Question

nine rules of contours are illustrated in figure 2.21. two additional rules are: (1) contours do not cross one another. (2) individual contours do not branch. contours appear to branch in cases of vertical cliffs, but the apparent branches are actually separate contour lines superposed on one another. contour interval - the succession of elevation values represented by contour lines is commonly graduated in some multiple of five or ten feet. the choice of contour interval depends on (a) the scale of the map, and (b) the magnitude of relief - which is the difference in elevation between the highest point and the lowest point within the map area. if the contour interval is too small for a particular area, contour lines will be overly crowded. if too large, there will be too few contour lines to adequately portray the topography. another thing: by convention, every fifth contour line is heavier in line weight than others. this difference makes it a bit easier to visually follow an individual contour across a map. and, it imparts a more obvious fabric to the map. q2.30 what is the contour interval shown in figure 2.21b? q2.31 in figure 2.21b, what is the relief between the lowest and highest contour lines? figure 2.21 the rules of contours. a. an oblique sketch of a land surface. b. a contour map illustrating the land surface shown in a.

Explanation:

Step1: Identify contour - value differences

Observe the contour - values in Figure 2.21B. The contour values are 80, 100, 120, 140, 160, 180.

Step2: Calculate the contour interval

The difference between consecutive contour values is constant. For example, \(100 - 80=20\), \(120 - 100 = 20\), etc. So the contour interval is 20.

Step3: Calculate the relief

The highest contour value in Figure 2.21B is 180 and the lowest is 80. The relief is the difference between the highest and lowest contour values. So, \(180-80 = 100\).

Answer:

Q2.30: 20
Q2.31: 100