---
title: "Bearings and local attraction explained"
subject: "Surveying I"
chapter: 4
key: "semester_3/surveying_i:bearings-and-local-attraction-terms"
source: https://www.bctengineer.com/q/semester_3/surveying_i/bearings-and-local-attraction-terms
site: BCT Engineering
---

# Bearings and local attraction explained

Surveying I · Chapter 4: The Compass

- Asked in: 2065 Shrawan, 7 marks; 2066 Bhadra, 7 marks (asked 2 times)
- Video: [Compass Surveying Explained in Simple Words | Types, Bearings, Local Attraction & applications ](https://www.youtube.com/watch?v=ODIy8lqM198) — Civil Engineering Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/bearings-and-local-attraction-terms
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4

## Question

What are quadrantal and whole circle bearings, fore and back bearings, and local attraction in compass survey? Explain.

## Short answer

Whole circle bearing measures clockwise from north 0–360°. Quadrantal bearing is acute angle from north/south toward east/west (e.g., N40°E). Fore bearing is along survey, back bearing opposite, differing by 180°. Local attraction is magnetic needle deviation from nearby objects, causing equal error at a station.

## Answer

#### Whole circle bearing (WCB)

The bearing of a line measured clockwise from the north end of the meridian, $0^\circ$ to $360^\circ$. Example: a line pointing south-west may have WCB $225^\circ$. This is the system of the prismatic compass.

#### Quadrantal bearing (QB), or reduced bearing

The acute angle ($0^\circ$ to $90^\circ$) between the line and the nearer end (north or south) of the meridian, measured towards east or west. It is written with the quadrant letters, e.g. N 40° E, S 30° W. This is the system of the surveyor's compass.

| WCB range | Quadrant | QB |
|---|---|---|
| $0^\circ$–$90^\circ$ | NE | N $\theta$ E, $\theta$ = WCB |
| $90^\circ$–$180^\circ$ | SE | S $\theta$ E, $\theta = 180^\circ - $ WCB |
| $180^\circ$–$270^\circ$ | SW | S $\theta$ W, $\theta$ = WCB $- 180^\circ$ |
| $270^\circ$–$360^\circ$ | NW | N $\theta$ W, $\theta = 360^\circ - $ WCB |

#### Fore bearing (FB) and back bearing (BB)

The bearing of a line in the direction of progress of the survey is its fore bearing; the bearing of the same line in the opposite direction is its back bearing. They differ by exactly $180^\circ$:

$$
\text{BB} = \text{FB} \pm 180^\circ
$$

Use $+$ if FB $< 180^\circ$ and $-$ if FB $> 180^\circ$. Example: FB of AB = $65^\circ 30'$, BB = $245^\circ 30'$.

#### Local attraction

The deviation of the magnetic needle from the magnetic meridian caused by magnetic substances near the station, such as iron objects, steel structures, power lines, or rocks containing iron ore. Bearings observed at an affected station are in error by the same amount.

- **Detection:** the FB and BB of a line differ by $180^\circ$ if neither end is affected; otherwise one or both stations are affected.
- **Correction:** (i) the line with FB − BB = $180^\circ$ is taken as free; bearings of the other lines are corrected station by station from it, or (ii) the included-angle method is used, because the angle at an affected station is not affected.

## Check yourself

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

1. How is a whole circle bearing measured?
   A. Acute angle from the nearer N or S end, 0° to 90°
   B. Clockwise from the north end of the meridian, 0° to 360°
   C. Anticlockwise from the north end, 0° to 360°
   D. Clockwise from the east end, 0° to 360°
   Answer: B. WCB is measured clockwise from north through 360° and is the prismatic compass system. (Key point: Whole circle bearing)

2. A line has WCB 225°. What is its quadrantal bearing?
   A. N 45° W
   B. S 45° E
   C. S 45° W
   D. S 135° W
   Answer: C. WCB 180°-270° lies in the SW quadrant, so QB = WCB - 180° = 45°, i.e. S 45° W. (Key point: Quadrantal bearing)

3. FB of AB = 65°30'. What is the BB?
   A. 114°30'
   B. 295°30'
   C. 65°30'
   D. 245°30'
   Answer: D. FB < 180° so add 180°: 65°30' + 180° = 245°30'. (Key point: Back bearing)

4. How is local attraction detected in a line?
   A. FB and BB do not differ by exactly 180°
   B. FB equals BB
   C. FB and BB sum to 360°
   D. The line is longer than 100 m
   Answer: A. If neither end is affected FB - BB = 180°; any other difference shows one or both stations are affected. (Key point: Detecting local attraction)

## Related in Surveying I

- [Local attraction with quadrantal bearings](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-quadrantal-bearings-s11-30w) — Surveying I, chapter 4
- [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, 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
- [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