Choosing a bicycle route from a contour map
A survey map at 1:50,000 shows villages A and B 8 cm apart. A metalled road runs between them but crosses a ridge at 480 m with steep 25° slopes on both sides. A footpath goes around the ridge through a gap at 260 m; it is 11 cm long on the map and crosses two streams. The contour interval is 20 m. A health worker must carry vaccines, which should stay below 8°C, from A to B within 3 hours. She can travel at 12 km/h on the metalled road and 6 km/h on the footpath. The student must convert map distances to ground distances, compare the routes, and recommend one, remembering that the map cannot show everything.
1. Convert the two route lengths to ground distances and calculate travel times.
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Scale 1:50,000 means 1 cm on the map = 50,000 cm on the ground = 0.5 km. Road: 8 cm × 0.5 km/cm = 4 km. Time = 4 ÷ 12 × 60 = 20 minutes. Footpath: 11 cm × 0.5 = 5.5 km. Time = 5.5 ÷ 6 × 60 = 55 minutes. Both are well within the 3-hour limit, so time alone does not decide the route. The difference is 35 minutes, but the road may be slower with a loaded bicycle on steep slopes. I would also add time for the two stream crossings on the footpath and for any walking uphill. The calculation assumes constant speeds, which is a simplification; on a 25° slope the bicycle may have to be pushed.
2. Interpret the contour evidence. Which route involves more climbing, and why might the shorter road still be slower?
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The road crosses a ridge at 480 m with 25° slopes on both sides. With a 20 m contour interval, the road must climb from the valley to 480 m and descend again; the contour lines will be close together, showing steepness. The footpath goes through a gap at 260 m, so its highest point is much lower and the climb is gentler. The road is only 4 km, but a loaded bicycle may have to be walked up the 25° slope, and braking on the descent is slow and risky. The footpath is longer at 5.5 km but has less climbing; however, it crosses two streams, which may be muddy or flooded. So map distance alone favours the road, but contour evidence favours the footpath for a loaded cyclist in dry weather.
3. Recommend a route and state one important limitation of the map.
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I would recommend the footpath in dry weather, because it avoids the 480 m ridge and its 25° slopes, and 55 minutes is well within the limit. The vaccines need a steady temperature, so a route that forces hard uphill effort and possible falls is less suitable. In heavy rain, the two stream crossings could become dangerous, and then the metalled road is safer despite the climb. The map limitation is that it cannot show the depth or speed of streams, the actual road surface, landslips, or whether the footpath is overgrown. A 20 m contour interval also hides small gullies and bumps. The health worker should check local conditions before choosing, and carry the vaccine cold box properly.