What is “local attraction” in the context of compass surveying?
- AThe deviation caused by the Earth’s magnetic poles shifting over time
- BThe error in a compass reading caused by nearby magnetic objects or anomaliesCorrect
- CThe difference between true north and magnetic north
- DThe phenomenon where a compass points directly to the geographic north pole
Solution
Concept
Definition of local attraction in compass surveying
Formula
NONE
Step-by-step solution
1. In compass surveying, local attraction refers to magnetic disturbances caused by artificial or natural magnetic sources. Answer: B
Explanation
Local attraction refers to the localized deflection of a compass needle away from the Earth's magnetic meridian due to external magnetic fields. This anomaly occurs when magnetic materials such as iron ore deposits, steel structures, or electrical cables are near the instrument. Thus, option B correctly defines local attraction as reading errors caused by nearby magnetic objects.
Why the other options are wrong
A) Shift in Earth's magnetic poles over time is known as secular variation. C) The difference between true north and magnetic north is magnetic declination.
Shortcut
Local attraction = Compass reading error caused by nearby magnetic objects.
Common mistake
Confusing local attraction caused by nearby magnetic objects with natural magnetic declination (Option C).
Correct answer: B) The error in a compass reading caused by nearby magnetic objects or anomalies