The Map Reading
You are on a navigation exercise with a map and compass. The map scale is 1:25,000. You are at grid point A (GR 123456). Your destination is grid point B (GR 789012). The straight-line distance on the map between A and B is 8 cm. There is a river between A and B that you must cross at a bridge. The bridge is located at grid point C (GR 456789), which is not on the straight line between A and B. You need to plan a route from A to B via the bridge. You estimate your walking speed is 4 km/h on flat terrain, but the terrain from A to C is hilly and will slow you to 3 km/h, while from C to B is flat. You have 3 hours of daylight left.
1. Calculate the real-world distances from A to C and C to B using the map scale, given that the map distances are 5 cm and 6 cm respectively.
Read the worked answer
Scale 1:25,000 means 1 cm on map = 25,000 cm = 0.25 km in reality. Distance A to C = 5 cm * 0.25 km/cm = 1.25 km. Distance C to B = 6 cm * 0.25 km/cm = 1.5 km. Total route distance = 2.75 km.
2. Estimate the total time required for the route and determine if you can reach B before dark.
Read the worked answer
Time A to C: distance 1.25 km at 3 km/h = 1.25/3 h = 0.4167 h = 25 minutes. Time C to B: distance 1.5 km at 4 km/h = 1.5/4 h = 0.375 h = 22.5 minutes. Total time = 47.5 minutes. This is well within 3 hours, so you can reach B before dark.