--- title: "Characteristics of contours with sketches" subject: "Surveying II" chapter: 4 key: "semester_4/surveying_ii:contour-characteristics-sketches" source: https://www.bctengineer.com/q/semester_4/surveying_ii/contour-characteristics-sketches site: BCT Engineering --- # Characteristics of contours with sketches Surveying II · Chapter 4: Contouring - Asked in: 2078 Poush, 6 marks; 2075 Baisakh, 5 marks; 2070 Bhadra, 8 marks; 2065 Kartik (old course), 6 marks; 2065 Chaitra (old course), 9 marks (asked 5 times) - Video: [Contour Lines | Characteristics Of Contour Lines | Contouring | Surveying | Civil Engineering |](https://www.youtube.com/watch?v=A3VVWVxbwNI) — Civil Inside - 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-sketches - Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-4 ## Question Explain the characteristics of contours with supporting sketches. ## Short answer Contours are imaginary closed lines joining points of equal elevation, never crossing except at overhanging cliffs. Closely spaced contours indicate steep slopes; widely spaced indicate gentle slopes. Concentric closed contours with higher values inside represent hills; lower inside depressions. They bend upstream in valleys and downstream on ridges, crossing ridge/valley lines at right angles. ## Answer A **contour** is an imaginary line joining points of equal elevation on the ground. Every point on a contour has the same RL (reduced level), and a contour is the line in which a level surface cuts the ground. #### 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. 7. **A set of concentric closed contours** with the higher value inside represents a hill; with the lower value inside it represents a depression (pond or pit). 8. **Contours bend as V or U shapes across a ridge and a valley.** For a ridge (spur) the bend of the contour points towards the lower ground; for a valley the bend points towards the higher ground. 9. **Contours of the same elevation may reappear** on the other side of a ridge or a valley, so one contour value can appear twice on a map. 10. **A contour cannot lie between two contours of higher (or lower) values** unless it closes on itself (hill or depression). 11. **A saddle (col)** is shown by the closed contours of two hills on opposite sides, with lower ground (valleys) on the other two sides; the saddle point lies at the neck between the hills. ```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 ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a contour? A. A line joining points of equal elevation, where a level surface cuts the ground B. A line of constant slope C. A line joining points of equal horizontal distance D. The vertical distance between two levels Answer: A. All points on a contour have the same RL; it is the line where a level surface meets the ground. (Key point: Definition) 2. Why do contours of different elevations not cross or unite, and when are they exceptions? A. One point cannot have two elevations; exceptions are a vertical cliff (merge) and an overhanging cliff or cave (cross) B. They can cross anywhere on steep slopes C. They merge on every ridge D. They cross at saddles Answer: A. A point on two contours would have two RLs, which is impossible except at a vertical cliff or overhang. (Key point: Crossing) 3. What does close spacing of contours indicate? A. A gentle slope B. A steep slope C. A flat plateau D. A depression Answer: B. Closely spaced contours mean a rapid change of elevation over a short distance, i.e. a steep slope. (Key point: Spacing) 4. How do contours bend across a ridge compared with a valley? A. Ridge: bend points towards lower ground; valley: bend points towards higher ground B. Ridge: bend points towards higher ground; valley: towards lower ground C. Both bend in the same direction D. Both cross at an angle of 45° Answer: A. For a ridge the V or U points downhill; for a valley it points uphill. Both cross contours at right angles. 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