--- title: "Direct contouring method, uses of contour map" subject: "Surveying II" chapter: 4 key: "semester_4/surveying_ii:direct-contouring-uses-contour-map" source: https://www.bctengineer.com/q/semester_4/surveying_ii/direct-contouring-uses-contour-map site: BCT Engineering --- # Direct contouring method, uses of contour map Surveying II · Chapter 4: Contouring - Asked in: 2071 Magh, 6 marks - Video: [Direct Method of Contouring | Use of Contour Surveying | Part I](https://www.youtube.com/watch?v=GJC_mRz7saI) — Salim K Tutorials - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/surveying_ii/direct-contouring-uses-contour-map - Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-4 ## Question Explain the direct method of contouring and write the uses of contour map. ## Short answer In direct method, staff readings are set to HI minus desired contour elevation; staff man moves until reading matches, then points pegged and located by plane table/theodolite. Contour maps are used to find elevations, design alignments with given gradient, compute earthwork and reservoir capacity, assess intervisibility, select sites, and plan drainage. ## Answer #### Direct method of contouring In the **direct method** the contours are located and marked directly on the ground, and the points are then surveyed and plotted. It is accurate but slow and costly, so it is used for small areas and large-scale maps. **Steps** 1. Establish control (traverse stations) and a benchmark in the area. 2. Set up a level at a convenient point, take a back-sight on the BM and find the height of instrument: $HI = RL_{BM} + BS$. 3. For a contour of RL $h$, the staff reading required is $r = HI - h$. A staff man moves up or down the slope until the staff reading equals $r$; that point lies on the contour. Mark it with a peg. 4. Find several points of the same contour, then move to the next contour (staff reading changed by the CI). 5. When the level is shifted, a new HI is found by sighting a fixed point (change point). 6. The pegs are then located by the **plane table, theodolite (tacheometer), chain or compass** from the control stations and plotted on the sheet. The points of equal RL are joined by a smooth curve. For steep ground a clinometer or a hand level may be used with a ranging rod. #### Uses of a contour map 1. To find the elevation of any point and the slope between two points from the map (without going to the field). 2. To draw the longitudinal section and cross-sections of a road, railway, canal or pipe line on paper. 3. To fix the best alignment of a road, railway or canal with a given gradient (contour gradient). 4. To find the intervisibility of two points (to decide if a signal station can be seen from another). 5. To calculate the capacity of a reservoir, the catchment area and the volume of earthwork (area between contours). 6. To select suitable sites for a dam, building, bridge, airport or a water tank, and to mark the drainage lines (watershed). 7. To find the quantity of cutting and filling for levelling a site and to plan irrigation and drainage layout. 8. To study the general topography (hills, valleys, ridges) of a large area, and for military purposes and town planning. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the direct method, how is a point on a contour of RL h located? A. The staff is moved until reading = HI - h, then pegged B. By interpolation of spot levels C. By measuring angle only D. By chaining along the slope Answer: A. The staff reading required is HI - h; the point is marked with a peg. (Key point: Direct method principle) 2. How is HI found from the BM? A. HI = RL of BM + back-sight B. HI = RL of BM - back-sight C. HI = RL of BM + fore-sight D. HI = BS - FS Answer: A. Back-sight on the BM gives HI = RL(BM) + BS. (Key point: Height of instrument) 3. The direct method is best for? A. Small areas and large-scale maps; it is accurate but slow and costly B. Large areas C. Small-scale maps D. Quick reconnaissance Answer: A. Because it is accurate but slow and costly, it suits small areas. (Key point: Suitability) 4. Which is a use of a contour map? A. Finding reservoir capacity and catchment area, and intervisibility of two points B. Measuring magnetic declination C. Setting out curves only D. Finding the weight of soil Answer: A. Contour maps give elevation, slope, alignment, intervisibility, capacity, earthwork and sites. (Key point: Uses of contour map) ## Related in Surveying II - [Methods of contouring and uses of contour maps](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontouring-methods-uses) — Surveying II, chapter 4 - [Contour characteristics and uses of contour map](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontour-characteristics-uses) — 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 - [Index contour and indirect contouring](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aindex-contour-indirect-method) — Surveying II, chapter 4 - [Contouring methods, direct method field procedure](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Acontouring-methods-direct-field-procedure) — 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 ## Related in other subjects - [Types and uses of EG map](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aeg-map-types-uses) — Engineering Geology II, chapter 1, asked 3×