--- title: "Contour characteristics, guide points A and B" subject: "Surveying II" chapter: 4 key: "semester_4/surveying_ii:contour-characteristics-six-guide-points" source: https://www.bctengineer.com/q/semester_4/surveying_ii/contour-characteristics-six-guide-points site: BCT Engineering --- # Contour characteristics, guide points A and B Surveying II · Chapter 4: Contouring - Asked in: 2080 Chaitra, 4+2 marks - Video: [Lec 1| Contour & Characteristics (Property) of Contour | Unit 3 Mapping & Sensing |BASIC CIVIL ENGG](https://www.youtube.com/watch?v=4O1XQvQfX9c) — Education Point Online - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/surveying_ii/contour-characteristics-six-guide-points - Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-4 ## Question 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. ## 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. ## Answer #### 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. ```text HILL DEPRESSION .--100--. .--100--. / .-110-. \ / .--90-. \ | / (120) \ | | / (80) \ | \ '-----' / \ '-----' / '-------' '-------' RL rises to the centre RL falls to the centre ``` ```text RIDGE (v points downhill) VALLEY (^ points uphill) 130 \ / 120 /\ \ / / \ 120 \ / 110 / \ \_/ / \ 110 \ / 100 / \ \___/ high ground at top high ground at top ``` ```text 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: $RL_A = 1000.25$ m, $RL_B = 1001.32$ m, distance on the map $AB = 5$ cm, CI = 0.5 m. Difference of level $= 1001.32 - 1000.25 = 1.07$ 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: $$ x = \frac{h_c - 1000.25}{1.07}\times 5\ \text{cm} $$ | Contour (m) | Height above A (m) | Distance from A (cm) | |---|---|---| | 1000.50 | 0.25 | $\frac{0.25}{1.07}\times 5 = 1.17$ | | 1001.00 | 0.75 | $\frac{0.75}{1.07}\times 5 = 3.50$ | ```text 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.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why do contours of different elevation not cross each other (except at an overhanging cliff or cave)? A. Because a point cannot have two elevations B. Because contours are always straight C. Because the CI would change D. Because contours must close inside the map Answer: A. All points on one contour share the same elevation, so a crossing point would have two elevations. (Key point: Contours not crossing) 2. RL_A = 1000.25 m, RL_B = 1001.32 m, CI = 0.5 m. Which contours lie between A and B? A. 1000.50 m and 1001.00 m B. 1000.00 m and 1001.50 m C. 1000.50 m, 1001.00 m and 1001.50 m D. 1000.25 m and 1001.32 m Answer: A. Multiples of 0.5 m between 1000.25 and 1001.32 are 1000.50 and 1001.00; 1001.50 is above B. (Key point: Contours between A and B) 3. What is the distance of a contour hc from A on the 5 cm line AB? A. (hc - 1000.25)/1.07 x 5 cm B. (1001.32 - hc)/1.07 x 5 cm C. (hc - 1000.25) x 5 cm D. (hc/1.07) x 5 cm Answer: A. With uniform slope, distance from A is proportional to height above A: x = (hc - RL_A)/(RL_B - RL_A) x 5 cm. (Key point: Interpolation formula) 4. How far from A is the 1001.00 m contour? A. 1.17 cm B. 2.50 cm C. 3.50 cm D. 4.67 cm Answer: C. Height above A = 0.75 m, so x = 0.75/1.07 x 5 = 3.50 cm. (Key point: Distance of 1001.00 m contour) 5. How far from A is the 1000.50 m contour? A. 0.25 cm B. 1.17 cm C. 2.34 cm D. 3.50 cm Answer: B. Height above A = 0.25 m, so x = 0.25/1.07 x 5 = 1.17 cm. 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