Question

Define: (i) Grid North, (ii) Magnetic Bearing.

Hint:

To convert a Magnetic Bearing to a Grid Bearing, you must adjust for the Magnetic Declination (the angle between Grid North and Magnetic North) using the formula: $$\text{Grid Bearing} = \text{Magnetic Bearing} \pm \text{Magnetic Variation}$$

Answer 1

Step 1: Defining (i) Grid North (GN):
Grid North is the direction of the vertical grid lines (Eastings) printed on a topographical map, pointing toward the top of the map sheet.
• Key Characteristics: Because maps are flat representations of a curved Earth, the grid lines do not converge at the geographic pole. Thus, Grid North deviates slightly from True North. This deviation is known as Grid Convergence.

Step 2: Defining (ii) Magnetic Bearing:
Magnetic Bearing is the horizontal angle measured clockwise between the Magnetic North line (as indicated by the compass needle) and the line of sight pointing to the target.
• Measurement: It is measured directly in the field using a prismatic liquid compass, which aligns with the Earth's magnetic field.