--- title: "Checking open traverse; Bowditch graphically" subject: "Surveying I" chapter: 4 key: "semester_3/surveying_i:open-traverse-check-bowditch" source: https://www.bctengineer.com/q/semester_3/surveying_i/open-traverse-check-bowditch site: BCT Engineering --- # Checking open traverse; Bowditch graphically Surveying I · Chapter 4: The Compass - Asked in: 2078 Kartik, 2+4 marks - Video: [Balancing of traverse using Bowditch rule](https://www.youtube.com/watch?v=hUn7pl7iZ0A) — Gayathri VG - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/open-traverse-check-bowditch - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4 ## Question How can an open traverse be checked during compass survey? Describe the Bowditch method of adjustment of a closed traverse graphically. ## Short answer An open traverse is checked by FB/BB, shots to landmarks, tie lines, and closing on known points. The Bowditch graphical adjustment: draw a base line equal to the perimeter, at its end erect a perpendicular equal to the closing error; ordinates from cumulative distance points to the line from start to top give station corrections applied parallel to the closing direction. ## Answer #### Checking an open traverse in compass survey An open traverse has no closing check, so extra observations are taken: 1. **Fore and back bearings** of every line are observed; FB − BB should be $180^\circ$ (detects local attraction). 2. **Cross-checks to a distant landmark:** a prominent object is sighted from several stations; plotted rays must meet at one point. 3. **Check lines (tie lines)** are measured between non-adjacent stations and compared with the plotted distance. 4. **Linking to known points:** the traverse is closed on a station of known position or bearing (link traverse) and the closure is checked. 5. **Repeat measurement** of lengths (forward and back). #### Graphical Bowditch adjustment of a closed traverse Bowditch's rule distributes the closing error in proportion to the lengths of sides, so the correction at a station is proportional to the distance travelled from the start. 1. Plot the traverse A-B-C-D-E-A′. The closing error is A′A. 2. Draw a base line AA′ equal to the perimeter and mark b, c, d, e at the cumulative distances AB, AB+BC, ... 3. Erect A′X perpendicular at A′ equal to the closing error and join AX. 4. Ordinates from b, c, d, e to AX give the corrections of B, C, D, E. 5. On the plan, draw through each station a line parallel to A′A and mark off these corrections; join the shifted points. ```text X . | . | . e' | . d' | | . c' | | | . b' | | | | A -----b-----c-----d-----e-----------A' (base = perimeter, marks at cumulative distances; A'X = closing error, drawn at right angles) ``` The corrected traverse closes at A. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why must an open traverse have extra checks? A. It is always accurate B. It has no bearings C. It has no closure to detect errors D. It uses no chain Answer: C. A closed loop shows errors automatically; an open traverse does not. (Key point: No closing check) 2. Which is a valid check on an open traverse? A. Doubling the scale B. Ignoring FB C. Using a different compass for each line D. Sighting a distant landmark from several stations; rays must meet at a point Answer: D. Cross-checks to a landmark, tie lines and link traverses give checks. (Key point: Check methods) 3. Bowditch's rule distributes the closing error: A. In proportion to the lengths of sides B. Equally among all sides C. Only to the last side D. In proportion to angles Answer: A. Correction is proportional to distance travelled from the start. (Key point: Bowditch rule) 4. After graphical adjustment the corrected traverse: A. Still ends at A' B. Closes at the starting point A C. Becomes an open traverse D. Loses its scale Answer: B. The shifted points join to form a closed figure. (Key point: Result) ## Related in Surveying I - [Closing error; plotting methods in compass traverse](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aclosing-error-plotting-methods) — Surveying I, chapter 4 - [Local attraction: AB 69°30′ compass traverse](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ab-69-30-reordered) — Surveying I, chapter 4 - [Closing error and graphical adjustment](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aclosing-error-graphical-adjustment) — Surveying I, chapter 4, asked 13× - [Corrected bearings of closed traverse PQRST](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aclosed-traverse-pqrst-correct-bearings) — Surveying I, chapter 4 - [Local attraction in closed traverse PQRSTP](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-pqrstp-188-45) — Surveying I, chapter 4 - [Interior angles and bearings, closed traverse ABCD](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Ainterior-angles-closed-traverse-104-30) — Surveying I, chapter 4 ## Related in other subjects - [Closed/open traverse, Bowditch's rule](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aclosed-open-traverse-bowditch-rule) — Surveying II, chapter 1, asked 2× - [Closed/open traverse, transit rule](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aclosed-open-traverse-transit-rule) — Surveying II, chapter 1, asked 2× - [Closed/open traverse, consecutive, independent coordinates](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aclosed-open-traverse-consecutive-independent) — Surveying II, chapter 1 - [Field measurements in traversing, closed/open traverse](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-field-measurements-closed-open) — Surveying II, chapter 1