Loci

3. Identifying an exact location

Required Resources

• Student Worksheet 3

Delivery

• Set the scene for this task with a brief discussion of the difficulties in navigating in poor visibility. It is clear that information and speed of response are key to success and that teamwork is the only way in which the ground can be covered.
• Highlight how often the rescuers have limited information to work with e.g. bearing, last seen heading on or co-ordinates in the range of, or a destination. Explain the need for multiple rescuers in such an exercise, not only speeding up the search but also for human reasons e.g. error, undulating terrain which reduces speed on foot and fatigue.
• Students work in teams using the information provided to brief the RAF Mountain Rescue Team searching for two hill walkers. These men left from a spot marked A, leaving specific information concerning their destination and planned journey time. However they are now overdue and weather conditions are worsening. Students should identify the area within which the rescuers should search, taking into account the average walking speed (circular loci). Students should draw all stages of this activity on the map.
• Part 1a encourages the students to look more closely at the map in front of them. They should observe that within the area of ground to be searched, much is water or forest. Walkers are unlikely to have entered the water and the forest areas marked are private plantations, not open to the public. Students should mark their map to eliminate these areas.
• To answer Part 2 you should provide students with additional information, not pre-printed on their sheet. A telephone call has been received from another hill walker. She saw the missing pair only half an hour previously and is able to shed some further light on their location. She was standing on the highest point of a mountain called Am Bathach and saw two men walking along the crest towards her. One appeared to be holding his chest as if in pain. Read out the following additional information:
  • Last seen following the ridge of Am Batach, 10km north of the Cluanie Inn (point A), exactly halfway between points B andC on the streams that run in the valleys either side of the mountain.
• In response to this information, students should draw a possible search line along the ridge of Am Batach, drawing a perpendicular bisector of the line BC using the points indicated. They should then identify the specific location of the hill walkers through convergent loci and the time taken to travel there on foot.
• Once students identify the convergent point of the angle bisector and circular loci, it should be explained that this is simply the focal area for the search. As their indicated walking speed is only an average one, the walkers may in fact be anywhere along the angle bisector loci.

Differentiation

Lower Ability:

Provide less able students with pre-drawn loci and ask them to indicate how each one was constructed and what information it provides.