---
title: "Local attraction with quadrantal bearings"
subject: "Surveying I"
chapter: 4
key: "semester_3/surveying_i:local-attraction-quadrantal-bearings-s11-30w"
source: https://www.bctengineer.com/q/semester_3/surveying_i/local-attraction-quadrantal-bearings-s11-30w
site: BCT Engineering
---

# Local attraction with quadrantal bearings

Surveying I · Chapter 4: The Compass

- Asked in: 2072 Chaitra, 8 marks
- Video: [Compass Survey | Local attractions & Bearing correction ||engineering survey|| CTEVT & BE Civil](https://www.youtube.com/watch?v=xRfah7U8Q8A) — Train Your Brain Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/local-attraction-quadrantal-bearings-s11-30w
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4

## Question

The following bearings are observed in a compass traverse survey.

| Line | AB | BC | CD | DE | EA |
|---|---|---|---|---|---|
| Fore Bearing | S11°30′W | N67°30′E | N32°15′E | S82°45′W | S50°15′W |
| Back Bearing | N13°00′E | S66°30′W | S30°30′W | N80°45′E | N53°00′E |

Apply necessary checks and determine the corrected bearings.

## Short answer

All lines show FB−BB≠180°, so all stations are suspected. The included-angle method is used; interior angles sum 540° with corrections. Starting from the most reliable line BC (mean N67°00′E), corrected fore bearings are AB S12°36′W, BC N67°00′E, CD N32°39′E, DE S84°48′W, EA S54°12′W.

## Answer

The bearings are first converted to whole circle bearings (FB of AB = S11°30′W = 191°30′, BC = 67°30′, CD = 32°15′, DE = S82°45′W = 262°45′, EA = S50°15′W = 230°15′). FB − BB = 178°30′, 181°00′, 181°45′, 182°00′ and 177°15′, so no line is free and **all stations are suspected**. The included-angle method is used, and the results are shown in quadrantal form.

Local attraction at a station is detected by comparing the fore bearing (FB) and back bearing (BB) of each line: if there is no local attraction at either end, $\text{FB} - \text{BB} = 180^\circ$ exactly.

#### Step 1: Check each line

| Line | FB | BB | FB − BB | Remark |
|---|---|---|---|---|
| AB | S 11°30′ W | N 13°00′ E | 178°30′ | Differs by −1°30′ |
| BC | N 67°30′ E | S 66°30′ W | 181°00′ | Differs by +1°00′ |
| CD | N 32°15′ E | S 30°30′ W | 181°45′ | Differs by +1°45′ |
| DE | S 82°45′ W | N 80°45′ E | 182°00′ | Differs by +2°00′ |
| EA | S 50°15′ W | N 53°00′ E | 177°15′ | Differs by −2°45′ |

#### Step 2: Included (interior) angles

The included angle at a station uses the FB of the line leaving it and the BB of the line arriving at it, both observed at the same station, so local attraction cancels in the angle.

The sum of the interior angles should be $(2n-4)\times 90^\circ = 540^\circ$.

| Station | Angle between | Observed | Corrected |
|---|---|---|---|
| A | AE and AB | 138°30′ | 138°24′ |
| B | BA and BC | 54°30′ | 54°24′ |
| C | CB and CD | 145°45′ | 145°39′ |
| D | DC and DE | 52°15′ | 52°09′ |
| E | ED and EA | 149°30′ | 149°24′ |

Sum observed = 540°30′; error = +0°30′; correction per angle = −0°06′ (equal distribution, since each angle is measured with the same care).

No line has FB − BB = 180°. Line BC has the smallest difference (+1°00′), so it is the most reliable; its adopted bearing is the mean of the FB and (BB ± 180°) = N 67°00′ E.

#### Step 3: Corrected bearings from the corrected angles

Rule used (in WCB): FB of next line = BB of previous line + interior angle (traverse run anticlockwise). Starting from BC = 67°00′ (BB 247°00′): CD = 247°00′ + 145°39′ − 360° = 32°39′, and so on round the traverse.

| Line | Observed FB | Correction | Corrected FB | Observed BB | Corrected BB |
|---|---|---|---|---|---|
| AB | S 11°30′ W | +1°06′ | S 12°36′ W | N 13°00′ E | N 12°36′ E |
| BC | N 67°30′ E | −0°30′ | N 67°00′ E | S 66°30′ W | S 67°00′ W |
| CD | N 32°15′ E | +0°24′ | N 32°39′ E | S 30°30′ W | S 32°39′ W |
| DE | S 82°45′ W | +2°03′ | S 84°48′ W | N 80°45′ E | N 84°48′ E |
| EA | S 50°15′ W | +3°57′ | S 54°12′ W | N 53°00′ E | N 54°12′ E |

Check: corrected FB − corrected BB = 180° for every line.

*Corrections are in the whole-circle sense (+ is clockwise).*

**Answer:** Corrected bearings (FB): AB = S 12°36′ W, BC = N 67°00′ E, CD = N 32°39′ E, DE = S 84°48′ W, EA = S 54°12′ W.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the whole circle bearing of S 50°15′ W?
   A. 230°15′
   B. 129°45′
   C. 309°45′
   D. 50°15′
   Answer: A. In the SW quadrant WCB = 180° + reduced bearing = 230°15′. (Key point: Conversion to WCB)

2. Differences from 180° are 1°30′, 1°00′, 1°45′, 2°00′ and 2°45′. Which line is taken as most reliable?
   A. AB
   B. DE
   C. BC
   D. EA
   Answer: C. BC has the smallest difference (1°00′), so its mean bearing N 67°00′ E is adopted. (Key point: Most reliable line)

3. The interior angles sum to 540°30′. What is the correction per angle?
   A. +0°06′
   B. -0°06′
   C. -0°30′
   D. -0°05′
   Answer: B. Error +30′ spread over 5 angles = 6′ each, subtracted. (Key point: Angle correction)

## Related in Surveying I

- [Local attraction, bearings AB 305°00′ (EA 45°)](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ea-305-00) — Surveying I, chapter 4, asked 2×
- [Local attraction, BC 79°30′ and DE 82°15′](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ab-191-30-bc-79-30) — 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
- [Local attraction, bearings AB 305°30′](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ea-bb-44-00) — Surveying I, chapter 4, asked 2×
- [Local attraction and true bearings, 1°30′E](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Acompass-closed-traverse-declination-1-30-east) — Surveying I, chapter 4
- [Local attraction and true bearings, 7°W](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-true-bearings-7w) — Surveying I, chapter 4

## Related in other subjects

- [Bearings of DE and EA in traverse ABCDE](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-abcde-bearings-de-ea) — Surveying II, chapter 1, asked 2×
- [Traverse missing length CD, bearing EA](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-missing-cd-length-ea-bearing) — Surveying II, chapter 1
- [Closed traverse missing EA bearing, BC length](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aclosed-traverse-abcdea-missing-ea-bc) — Surveying II, chapter 1
- [Bearings of BC and CD in traverse ABCDE](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-abcde-bearings-bc-cd) — Surveying II, chapter 1, asked 2×