--- title: "Field sketch and mapping by linear measurement" subject: "Surveying I" chapter: 3 key: "semester_3/surveying_i:chain-field-sketch-mapping" source: https://www.bctengineer.com/q/semester_3/surveying_i/chain-field-sketch-mapping site: BCT Engineering --- # Field sketch and mapping by linear measurement Surveying I · Chapter 3: Chain Survey - Asked in: 2061 Baisakh, 8 marks - Video: [Field Survey Fridays - The Structure Of Field Drawings](https://www.youtube.com/watch?v=refSYc4T0V8) — Redefined Horizons Learning - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/chain-field-sketch-mapping - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-3 ## Question Make a field sketch for chain survey and explain the complete process of mapping by linear measurement only. ## Short answer A field sketch is a freehand key plan showing stations and lines. Mapping by linear measurement: field work includes reconnaissance, station marking, chaining triangle sides, taking offsets, and booking; office work includes choosing scale, plotting the triangle framework by intersecting arcs, plotting offsets, checking, and inking. ## Answer #### Field sketch A neat, freehand **key plan** (index sketch) of the area is prepared first. It shows the boundary, main details, the stations (A, B, C, D) and the survey lines with their names. The lines are numbered in the order in which they will be chained. ```text Key plan (not to scale) C /|\ [House] / | \ / | \ Pond (o) A---D---B ----> road (CD = check line) ``` #### Complete process of mapping by linear measurement only **Field work** 1. **Reconnaissance** and selection of stations A, B, C ... so that the triangles are well-conditioned (angles between $30^\circ$ and $120^\circ$). 2. Mark the stations with pegs and draw the key plan. 3. Fix the base line (the longest line, on level ground) and the check lines. 4. **Chain the lines.** Measure each side of every triangle (AB, BC, CA) and the check line CD. 5. **Take offsets** to the details: perpendicular offsets by tape with a cross-staff or optical square; oblique offsets (ties) for hidden or distant objects. 6. **Book** all measurements in the field book (from the bottom upwards). **Office work** 1. Choose a scale (for example 1:500) and compute the length of each line on paper. 2. Plot the base line AB first. Then plot C by intersecting arcs of radii AC and BC (to scale) drawn from A and B. 3. Plot the check line CD and compare its scaled length with the field value to detect errors. 4. Plot the offsets from the chain lines using the chainages and offset lengths, and join the plotted points to get the boundaries and details. 5. Ink the plan and add the north line, scale, title and legend. Thus, the whole map is made from linear measurements only, since a triangle is fixed by the lengths of its sides, and details are fixed by offsets and ties. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the key plan (index sketch) show? A. Contours and levels B. Magnetic bearings of lines C. Boundary, main details, stations and the survey lines D. The final inked map Answer: C. It is a freehand guide to the survey made before chaining. (Key point: Key plan) 2. How is the base line chosen? A. The shortest line near the boundary B. Any line over the pond C. The line with the most obstacles D. The longest line, on level ground Answer: D. It carries the framework so it should be long and easy to chain. (Key point: Base line) 3. How is the position of station C plotted from the base line AB? A. Intersect arcs of radii AC and BC (to scale) from A and B B. Measure the angle at A with a protractor C. Drop a perpendicular from the north line D. Use the bearing of AC Answer: A. The three sides fix the triangle. (Key point: Plotting point C) 4. What is the use of check line CD? A. Replace line AB B. Compare its scaled length with the field value to detect errors C. Locate the north D. Increase the area Answer: B. A mismatch indicates a mistake in the framework. (Key point: Role of check line) ## Related in Surveying I - [Field book and obstacles in chain survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Afield-book-and-obstacles) — Surveying I, chapter 3 - [Obstacles; field sketch for detail survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacles-and-field-sketch) — Surveying I, chapter 3 - [Obstacles in chain survey and remedies](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacles-chain-survey) — Surveying I, chapter 3, asked 4× - [Chain survey principle and operations](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Achain-principle-and-field-procedure) — Surveying I, chapter 3, asked 2× - [Principle of chain survey; types of offsets](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Achain-principle-and-offsets) — Surveying I, chapter 3 - [Field procedure of chain surveying](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Afield-procedure-chain-survey) — Surveying I, chapter 3, asked 4× ## Related in other subjects - [Resource mapping and ethnographic survey](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aresource-mapping-ethnographic) — Technology, Environment and Society, chapter 2 - [Linear chain polymer; sulphur-based inorganic polymers](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alinear-polymer-sulphur-inorganic) — Engineering Chemistry, chapter 4 - [AET versus PET, field measurement of ET](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Aaet-pet-measurement) — Engineering Hydrology, chapter 3 - [Field of short linear quadrupole on axis](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aquadrupole-axis-field) — Engineering Physics, chapter 7