True Bearing (Grade 12 NSC Matric Geography): Revision Notes
True Bearing
What is true bearing?
True bearing is a fundamental concept in mapwork that helps us determine the exact direction from one point to another. Think of it as a precise way to describe which way you need to face when looking from one location to another on a map.
True bearing is the angle measured clockwise from true north (0°). True north is the direction towards the geographical North Pole, which appears as a vertical line pointing upwards on topographic maps.
Understanding true bearing is essential for navigation, mapwork calculations, and interpreting topographic maps accurately. It forms part of a broader set of mapwork calculations that also includes magnetic declination, magnetic bearing, position calculations, and map sheet references.
True bearing is one of the most fundamental skills in mapwork. Once you master this concept, you'll find it much easier to tackle more complex navigation problems and map interpretation tasks.
How to measure true bearing
When you need to find the true bearing from point A to point B, you're essentially measuring how many degrees you need to turn clockwise from north to face point B when standing at point A.
The systematic approach to measuring true bearing requires precision and careful attention to the correct sequence of steps. This method works consistently for any two points on a topographic map, regardless of their relative positions.
Worked Example: Step-by-step method for measuring true bearing
Here's the systematic approach to measure true bearing from point A to point B:
Step 1: Draw a straight line connecting point A and point B on your map. This line represents the direction you want to measure.
Step 2: Draw a north line through point A (this is your point of measurement). This north line should point towards true north and pass through point A.
Step 3: Place the centre (0) of your protractor at point A, with the mark aligned at the top of the north line you drew.
Step 4: Moving in a clockwise direction from , read the angle where the line connecting A and B intersects with your protractor scale.
Critical Direction Rule
Always remember to move to the right (clockwise) when measuring true bearing. This is crucial because true bearing is specifically defined as a clockwise measurement from north. Moving anticlockwise would give you an incorrect reading.
Practice example
Practical examples using trigonometric stations and spot heights are common in mapwork exercises, as these are standard features found on topographic maps that provide clear reference points for calculations.
Worked Example: Calculating True Bearing
Activity: Calculate the true bearing from trigonometric station 8 to spot height 110.
Solution approach:
- Locate both points on the map
- Apply the four-step method described above
- Measure the clockwise angle from north
Answer: The result would typically be expressed in degrees, such as or similar, depending on the specific positions of the points.
Remember: Always identify your starting point (trigonometric station 8) and your target point (spot height 110) clearly before beginning your measurement.
Understanding magnetic declination
While our focus is on true bearing, it's important to understand the relationship between true north and magnetic north for complete mapwork proficiency.
Magnetic declination is the angle between true north and magnetic north. This concept becomes relevant because:
- True north points to the geographical North Pole
- Magnetic north points to the magnetic North Pole (which moves over time)
- The angle between these two directions varies depending on your location and changes over time
- Maps show the magnetic declination for the year they were drawn
- This information appears on the left-hand side or bottom of topographic maps
Understanding magnetic declination is crucial when working with compass bearings in the field, as most compasses point to magnetic north rather than true north. You'll need this information when converting between true bearing and magnetic bearing calculations.
Exam tips for true bearing questions
Successful performance in true bearing questions requires attention to detail and consistent application of the correct method. Here are essential strategies for exam success:
Essential Exam Strategies
- Always check that you're measuring from the correct point (the "from" point in the question)
- Ensure your north line is truly vertical and pointing upwards
- Double-check that you're measuring clockwise, not anticlockwise
- In exams, answers are usually given to the nearest degree
- Practice identifying trigonometric stations (marked with triangles) and spot heights (elevation points) on maps
- Remember that true bearing can range from to , where and both represent due north
Key Points to Remember:
- True bearing is always measured clockwise from true north ()
- The four-step method ensures accurate measurement: draw connecting line, draw north line, position protractor, measure clockwise
- Always move to the right (clockwise) when taking measurements
- True bearing helps determine exact direction between any two points on a map
- Understanding magnetic declination is important for converting between true and magnetic bearings