Seven Point Five Kilometres by 14:00: Route Choice on a 1:50,000 Sheet
You are a cadet section commander on a map-reading exercise with ten cadets, on a Survey of India 1:50,000 sheet with a contour interval of 20 m, 2 cm grid squares and a magnetic declination of 0°40′ east. You are at the road junction in grid square 4527 at 11:10. The village objective is in grid square 4530. From the map: a metalled road runs 7.5 km to the village and crosses a stream on a bridge marked class 3; a hill track climbs about 120 m over 5.2 km and rejoins the road 400 m short of the village; a dry stream bed gives a flat 6.4 km route but narrows to a gorge at one point. Two cadets are moving slowly on turned ankles and cannot manage broken ground. The day is hot and clear and you must be at the village by 14:00. Your compass bearing to the village is 118° grid.
1. Choose the route and justify it with map evidence and a time calculation.
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Chosen: the metalled road, with conditions attached.
- Road: 7.5 km. Ten cadets with two bad ankles on a firm surface can hold about 3 km/h, giving 2 h 30 min, plus one 15-minute halt = 2 h 45 min. Start 11:10, arrive about 13:55 - inside the deadline, but with almost no margin.
- Hill track: 5.2 km shorter, but 120 m of climb on broken ground with two slow cadets means about 1.8 km/h plus climb time - roughly 3 hours, arriving about 14:15. Rejected: fails the deadline and risks the ankle injuries worsening far from a road.
- Dry stream bed: 6.4 km and flat, about 2 h 10 min on paper, but the gorge is a single point where two injured cadets must be lowered or helped through, and a dry bed in a hot day can carry water after hill rain. Rejected as the main route, retained as an emergency alternative only if the bridge is out and the bed is seen to be dry.
Conditions: start immediately, no kit inspection; the two ankle cases walk in the middle of the file with the heaviest cadet's load redistributed; a 15-minute halt at the halfway point; two fit cadets move ahead to the bridge at 4 km/h to inspect and report back.
2. Convert the bearing to magnetic, give the back bearing, and explain why the class 3 marking on the bridge matters.
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Conversion: declination is 0°40′ east, so it is added to a grid bearing.
- Magnetic bearing = 118° + 0°40′ = 118°40′, called 119° in practice.
- Back bearing (magnetic) = 118°40′ + 180° = 298°40′, about 299°. This is the bearing you would set to return to the junction, and the one to give a search party coming towards you.
Why class 3 matters: the bridge is load-classified, so it will take a jeep or an ambulance but not an arbitrarily heavy vehicle. It decides two things on this route: whether a vehicle can be brought forward to lift the two ankle cases the last stretch, and whether an evacuation by road is possible at all if someone is hurt badly. A route chosen on distance alone that ends at an unusable bridge is not a route.
One precaution: the declination is small but not zero, and on a 7.5 km leg a one-degree error is over 100 m of lateral drift - enough to miss a junction. The bearing is a check, not a substitute for reading the map and the ground.
3. What will you confirm on the ground before committing the whole party, and what will you do if the bridge is closed?
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Confirm before committing:
- The junction itself and the road's direction of travel, checked against the map rather than assumed.
- The bridge and its class plate, and whether a closure or weight notice is posted.
- The side turning where the hill track rejoins the road, marked mentally as the fallback, and the point where the dry stream bed leaves the road.
- Any stream depth or recent rain evidence, and the first water point.
If the bridge is closed:
- Do not commit the party onto the alternative on assumption. Send the two ahead cadets a short way into the stream bed to confirm it is dry and that the gorge is passable for slow walkers.
- If it is not confirmed within a set time - say 20 minutes - halt the party in shade at the road and report by telephone to the exercise control, stating position, numbers and the problem, and request a vehicle from the far side.
- Only if the bed is confirmed passable does the party move, in single file, with the ankle cases between fit cadets.
Reasoning: the deadline is a constraint, not an order to take eleven people into an unverified gorge. Reporting late is a failure of the exercise; a casualty in a gorge is a failure of judgement.