--- title: "Principles of surveying; scales used" subject: "Surveying I" chapter: 1 key: "semester_3/surveying_i:principles-and-scales-used" source: https://www.bctengineer.com/q/semester_3/surveying_i/principles-and-scales-used site: BCT Engineering --- # Principles of surveying; scales used Surveying I · Chapter 1: Introduction - Asked in: 2057 Chaitra, 6 marks - Video: [Lecture-3 |Principle of surveying, scales and shrinkage of maps| by- SKJ](https://www.youtube.com/watch?v=Wu-AUck4zN8) — Surveying in Civil Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/principles-and-scales-used - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-1 ## Question Explain what the principles of surveying are. Write the various scales used in surveying. ## Short answer The main principles are working from whole to part and fixing a point by at least two independent measurements. Scales used include plain, diagonal, vernier, comparative, scale of chords, scale of time or speed, and isometric scale. ## Answer #### Principles of surveying 1. **Working from whole to part.** A precise control framework is made over the whole area first; the details are then surveyed inside it. Errors are thus localised and do not accumulate. 2. **Fixing a point by at least two independent measurements** from known points: two distances, two angles, or one angle and one distance (or an offset and a chainage). A third measurement is taken as a check. A survey is also carried out with checks on all measurements and with accuracy suited to the purpose. #### Scales used in surveying A scale is the ratio of a length on the map to the corresponding length on the ground. It can be expressed as a representative fraction (RF), e.g. 1/50,000, a statement (1 cm = 500 m) or a graphical scale. 1. **Plain scale.** A line divided into main divisions and sub-divisions; it reads two units (e.g. metres and decimetres). 2. **Diagonal scale.** Reads three units (e.g. 100 m, 10 m and 1 m) using diagonal lines and the principle of similar triangles. 3. **Vernier scale.** A sliding scale that reads a fraction of the smallest main division. Least count = value of 1 main division / number of vernier divisions. 4. **Comparative scale.** Two scales with the same RF but different units, such as a metric and a British scale on one map. 5. **Scale of chords.** Used for plotting and measuring angles when no protractor is available. 6. **Scale of time or speed.** Used when time is to be measured from distance travelled at a constant speed. 7. **Isometric scale.** Used for isometric drawings. By size, maps are large scale (1:500 to 1:5000, used for detailed plans), medium scale and small scale (1:50,000 and smaller, used for atlases). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is the 'working from whole to part' principle followed? A. It lets the details be measured with the most precise instruments B. Errors do not accumulate, and a mistake in one part stays inside that part C. It removes the need to check measurements D. It makes the survey cheaper because no control stations are required Answer: B. A precise control framework is fixed first and details are fitted inside it, so errors are localised instead of adding up. (Key point: Why whole to part) 2. How should a new point be fixed according to the second principle? A. By one measurement from one fixed point B. By measuring only angles at the new point itself C. By estimating its position by eye and checking later D. By at least two independent measurements from points already fixed Answer: D. A point needs at least two independent measurements (distances, angles, or an offset and chainage) from known points. (Key point: Two measurements) 3. The least count of a vernier scale equals A. value of 1 main division divided by the number of vernier divisions B. the number of main divisions times n C. the length of the scale D. value of the vernier divided by 2 Answer: A. Least count = main division value / n. (Key point: Vernier) 4. A comparative scale is A. a scale for measuring time B. a scale drawn for isometric views C. two scales with the same RF but different units D. a scale for plotting angles Answer: C. Such as metric and British scales on one map. 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