Local attraction in compass surveying may exist due to the presence of magnetic substances near the instrument.

Explanation:

Local attraction refers to the phenomenon where the magnetic needle of a compass is influenced by nearby magnetic substances, resulting in inaccurate readings. This can significantly affect the accuracy and reliability of compass surveying, which relies on the proper alignment of the compass needle with the magnetic meridian.

The presence of magnetic substances near the compass instrument can create a magnetic field that interferes with the Earth's magnetic field, thereby causing the needle to deviate from its true north direction. This can lead to errors in determining the azimuth or bearing of a line, which can subsequently affect the accuracy of the survey measurements.

Here are some key points explaining why the correct answer is option D:

1. Magnetic substances: Magnetic substances such as iron ore, steel structures, underground pipes, electrical wires, or even nearby magnetic instruments can generate their own magnetic fields. These fields can attract or repel the compass needle, causing it to point in a different direction.

2. Magnetic field interaction: When a compass is placed near magnetic substances, the magnetic fields of both the Earth and the substances interact with each other. Depending on the strength and orientation of these fields, the compass needle may experience a force that pulls or pushes it away from its true north direction.

3. Deviation in readings: The presence of magnetic substances can cause the compass needle to deviate from its intended alignment. This deviation can be random and unpredictable, making it difficult to compensate for in surveying measurements.

4. Effects on levelling: Local attraction can also affect levelling operations, where a compass is used to determine the horizontal direction. If the compass needle is influenced by nearby magnetic substances, the levelling readings can be incorrect, leading to errors in determining elevations and slope angles.

In conclusion, the presence of magnetic substances near a compass instrument can result in local attraction, causing the compass needle to deviate from its true north direction. Surveyors must be aware of this potential source of error and take necessary precautions to minimize its impact on survey measurements.