---
title: "Define magnetic declination"
subject: "Surveying I"
chapter: 4
key: "semester_3/surveying_i:define-magnetic-declination"
source: https://www.bctengineer.com/q/semester_3/surveying_i/define-magnetic-declination
site: BCT Engineering
---

# Define magnetic declination

Surveying I · Chapter 4: The Compass

- Asked in: 2081 Baisakh, 1 marks
- Video: [Declination in Compass Surveying - Solved Problems](https://www.youtube.com/watch?v=h0SXXYUXVwc) — Stan Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/define-magnetic-declination
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4

## Question

Define magnetic declination.

## Short answer

Magnetic declination is the horizontal angle between the true meridian and the magnetic meridian at a point. It is east (positive) when magnetic north is east of true north, and west (negative) when west. True bearing = magnetic bearing + declination (east +, west –).

## Answer

**Magnetic declination** is the horizontal angle between the true (geographic) meridian and the magnetic meridian at a place. It is **east** (positive) when the magnetic north lies to the east of true north and **west** (negative) when it lies to the west. True bearing = magnetic bearing + declination (east $+$, west $-$).

## Check yourself

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

1. Magnetic declination is the angle between:
   A. Fore bearing and back bearing
   B. True meridian and magnetic meridian
   C. Magnetic meridian and a survey line
   D. Two survey lines
   Answer: B. It is the horizontal angle between true and magnetic meridians at a place. (Key point: Definition)

2. Declination is east (positive) when:
   A. Magnetic north lies west of true north
   B. The needle is attracted by iron
   C. Magnetic north lies east of true north
   D. The line points east
   Answer: C. East declination means magnetic north is east of true north. (Key point: East declination)

3. If magnetic bearing = 50° and declination is 3° west, the true bearing is:
   A. 53°
   B. 50°
   C. 57°
   D. 47°
   Answer: D. True = magnetic + declination (east +, west -) = 50° - 3° = 47°. (Key point: True bearing formula)

## Related in Surveying I

- [Variations in magnetic declination](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Avariations-in-magnetic-declination) — Surveying I, chapter 4
- [Quadrantal/WCB; declination, isogonic, agonic](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Abearings-declination-isogonic-agonic) — Surveying I, chapter 4
- [Corrected and true bearings, 5°E declination](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-true-bearings-5-deg) — Surveying I, chapter 4