Direction, Bearing, and Magnetic Bearing (Grade 10 NSC Matric Geography): Revision Notes

Direction, Bearing, and Magnetic Bearing

Understanding direction and compass points

Direction helps us describe where one place is located in relation to another place. When we look at maps, we use a system based on compass points to give clear directions.

The traditional compass system uses 16 different directional points. These include the four main directions (North, South, East, West) and twelve additional points like Northeast, Northwest, Southeast, and Southwest. This system provides a general way to describe direction, but it's not always precise enough for detailed navigation work.

What is bearing?

Bearing provides a much more accurate way to indicate direction than using compass points alone. Instead of just 16 compass directions, the bearing system uses a full 360-degree circle to pinpoint exact directions.

Here's how bearing works:

• We measure angles in degrees (°) from $0°$ to $360°$
• All measurements start from north ($0°$)
• We always measure clockwise around the circle
• East is at $90°$, South is at $180°$, and West is at $270°$

Measuring bearing step by step

To measure bearing between two places on a map, follow these steps:

1. Connect the points: Join the two locations with a straight pencil line on your map
2. Draw a north-south line: Draw a line running north-south through your starting point (the 'from' location)
3. Position your protractor: Place the centre of your protractor on your starting point, making sure the north-south line passes through $0°$ on your protractor
4. Measure clockwise: Measure the angle clockwise from north ($0°$) to your destination line
5. Read the bearing: The measurement where your line crosses the protractor scale gives you the true bearing

This measurement gives you what we call the true bearing - the angle measured from True North.

True bearing explained

True bearing uses True North as its reference point. True North represents the geographical North Pole - the exact point where all the longitude lines meet on Earth. When we measure bearing on a map, we use True North as our starting point.

Magnetic bearing and magnetic declination

In real-world navigation, however, things become more complicated. When explorers and navigators use an actual compass in the field, the compass needle doesn't point to True North. Instead, it points to magnetic north.

Magnetic north refers to the northern magnetic pole of our planet. This magnetic pole is located west of True North and constantly moves slowly across the Arctic region. The angle between True North and magnetic north is called magnetic declination.

Magnetic declination varies depending on your location on Earth and changes gradually over time. Topographic maps usually indicate the magnetic declination for that area and the year it was measured.

Calculating magnetic bearing

Sometimes you need to convert between true bearing and magnetic bearing. This becomes necessary when you're working with both map measurements (true bearing) and compass readings (magnetic bearing).

The relationship is:

$\text{Magnetic bearing} = \text{True bearing} + \text{Magnetic declination}$

Here's how to calculate current magnetic declination when you know historical data:

1. Start with historical declination: Find the magnetic declination for a past year
2. Calculate time difference: Work out how many years have passed since that measurement
3. Apply annual change: Multiply the yearly change rate by the number of years
4. Determine current declination: Add or subtract the total change from the historical declination

Remember!