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Contour characteristics, guide points A and B

Short answer

Contours are closed curves, all points on a contour have same elevation, they never cross (except overhanging cliff), closely spaced contours indicate steep slope, they cross ridges/valleys at right angles, and concentric closed contours indicate hill or depression. For the given points, difference in level is 1.07 m, contours at 1000.50 m and 1001.00 m lie on AB. By proportion, distance from A: 1000.50 m contour is 1.17 cm, 1001.00 m contour is 3.50 cm.

Explain the characteristics (important any six) of contours with suitable sketches. RL of two guide points A and B are 1000.25 m and 1001.32 m. The distance between these guide points in a topo map is 5 cm. Find the distance of all the contours that lies on line AB from guide point A if the contour interval is 0.5 m.

Six important characteristics of contours

  1. Contours are closed curves. Every contour must close on itself, either inside the map or outside it. It cannot start or end abruptly.
  2. All points on a contour have the same elevation.
  3. Contours never cross each other, except at an overhanging cliff or a cave. Two contours of different elevation cannot meet or cross because one point cannot have two elevations.
  4. Contours of different elevations do not unite to form one line, except at a vertical cliff, where they coincide and appear as one line.
  5. Closely spaced contours indicate a steep slope; widely spaced contours indicate a gentle slope. Equally spaced contours indicate a uniform slope, and straight, equal and parallel contours indicate an inclined plane.
  6. Contours cross ridge lines and valley lines at right angles. The direction of the steepest slope is at right angles to the contour.
        HILL                    DEPRESSION
      .--100--.                .--100--.
     / .-110-. \              / .--90-. \
    | / (120) \ |            | /  (80)  \ |
     \ '-----' /              \ '-----' /
      '-------'                '-------'
   RL rises to the centre     RL falls to the centre

   RIDGE (v points downhill)     VALLEY (^ points uphill)
      130  \   /                    120     /\
            \ /                           /  \
      120  \   /                    110   /    \
            \_/                          /      \
      110  \     /                  100 /        \
            \___/
   high ground at top            high ground at top

   Steep slope      Gentle slope      Uniform slope
   (close)          (wide apart)      (equal spacing)
   ----100          ----100           ----100
   ----101                            ----101
   ----102                            ----102
   ----103          ----101           ----103

Distances of contours from guide point A

Given: RLA=1000.25RL_A = 1000.25 m, RLB=1001.32RL_B = 1001.32 m, distance on the map AB=5AB = 5 cm, CI = 0.5 m.

Difference of level =1001.32−1000.25=1.07= 1001.32 - 1000.25 = 1.07 m.

Contours lying between A and B (multiples of 0.5 m): 1000.50 m and 1001.00 m (the next one, 1001.50 m, is above B).

The slope is taken as uniform, so the distance from A is proportional to the height above A:

x=hc−1000.251.07×5 cmx = \frac{h_c - 1000.25}{1.07}\times 5\ \text{cm}
Contour (m)Height above A (m)Distance from A (cm)
1000.500.250.251.07×5=1.17\frac{0.25}{1.07}\times 5 = 1.17
1001.000.750.751.07×5=3.50\frac{0.75}{1.07}\times 5 = 3.50
   A(1000.25)   1000.50      1001.00        B(1001.32)
   o-------------|-------------|-------------o
   0          1.17 cm      3.50 cm        5 cm

Answer: the 1000.50 m contour is 1.17 cm and the 1001.00 m contour is 3.50 cm from A.

✓ Answer checked by Claude Opus 5.5 (high effort)

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