--- title: "Contour terms and characteristics with sketch" subject: "Surveying II" chapter: 4 key: "semester_4/surveying_ii:contour-terms-characteristics" source: https://www.bctengineer.com/q/semester_4/surveying_ii/contour-terms-characteristics site: BCT Engineering --- # Contour terms and characteristics with sketch Surveying II · Chapter 4: Contouring - Asked in: 2074 Bhadra, 6 marks; 2073 Magh, 6 marks; 2072 Asoj, 8 marks (asked 3 times) - Video: [WHAT IS CONTOUR | CHARACTERSTICS AND METHODS | CIVIL ENGINEERING | MINING ENGINEERING | MINING WORLD](https://www.youtube.com/watch?v=PQfr1LABZWg) — Mining World - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/surveying_ii/contour-terms-characteristics - Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-4 ## Question Define contour interval, contour gradient and index contour. Explain the main characteristics of contours with neat sketch. ## Short answer Contour interval is the constant vertical distance between successive contours. Contour gradient is a line of uniform slope cutting contours at equal horizontal equivalent. Index contour is every fifth contour, thicker and labeled. Key characteristics: contours are closed, never cross; closely spaced means steep slope; concentric closed with higher inside = hill; bend upstream in valleys, downstream on ridges. ## Answer #### Definitions - **Contour interval (CI)** is the constant vertical distance between two consecutive contours, for example 1 m or 5 m. It is the same over one map. - **Contour gradient** is the line of constant slope (uniform gradient) that cuts the contours at the same horizontal equivalent. It is laid on the ground to fix the route of a road, railway, canal or pipe line. The gradient = CI / HE = 1 in (HE/CI). - **Index contour** is every fifth contour (for example every 5th line when CI = 2 m, giving 10 m, 20 m, 30 m ...) drawn as a thicker line and labelled with its RL, so that the map can be read quickly. The other contours are called **intermediate (minor) contours**. #### Main 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). ```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 gradient and how is it expressed? A. A line of constant slope that cuts the contours at the same horizontal equivalent; gradient = CI/HE B. The vertical distance between contours C. Every fifth contour drawn thicker D. A line along which the slope changes Answer: A. A contour gradient is a uniform slope line used to fix routes; gradient = CI/HE = 1 in (HE/CI). (Key point: Contour gradient) 2. Which contours are index contours? A. Every contour that closes on itself B. Every fifth contour, drawn thicker and labelled with its RL C. The contours at the edge of the map D. Contours of the lowest RL Answer: B. Every fifth contour is thicker and labelled so that the map can be read quickly; the others are intermediate contours. (Key point: Index contour) 3. Concentric closed contours with higher values inside represent what? A. A depression B. A hill C. A saddle D. A valley Answer: B. If RL rises towards the centre, it is a hill; if it falls towards the centre, it is a depression. (Key point: Hill or depression) 4. What is true of the contour interval on one map? A. It varies with the slope B. It is the constant vertical distance between consecutive contours C. It is the horizontal distance between contours D. It equals the index interval Answer: B. CI is constant over one map, whereas the horizontal equivalent varies with slope. (Key point: Contour interval) ## Related in Surveying II - [Contour gradient, index contour, interval factors](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-gradient-index-interval-factors) — Surveying II, chapter 4 - [Contour interval, index contour, plotting, uses](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-interval-index-plotting-procedure-uses) — Surveying II, chapter 4 - [Contour index, fixing contours between 1240.12 and 1264.32](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-index-fixing-uniform-slope-points) — Surveying II, chapter 4 - [Contour gradient and characteristics](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-gradient-characteristics) — Surveying II, chapter 4 - [Contour interval, index contour, why never cross](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-interval-index-plotting-never-cross) — Surveying II, chapter 4 - [Contour interval, index contour, contouring methods](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-interval-direct-indirect-methods) — Surveying II, chapter 4 ## Related in other subjects - [Main characteristics of 3d transition elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3A3d-characteristics) — Engineering Chemistry, chapter 5