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When estimating trip times, remember that an inch on your topo can equal a mile of walking (flat terrain) or much more (hilly terrain). Think of it this way: If you were to put a mountain between map points A and B, your actual hiking distance would increase, even though points A and B are still only an inch apart on the map.
You can determine actual distance in mountainous country by using simple high school trigonometry. First, estimate slope percent for the part of your route in question by dividing the vertical by the horizontal distance. For example, a 2,000-foot climb within a 1-mile horizontal distance is: 2,000 / 5,280 = .378, or 38 percent.
Using the table below, you can then translate percent to degrees of slope angle, which are easier for most people to visualize. Once you convert to degrees, multiply your traced map mileage by the factors in the third column. In this case, 38 percent equals a 20-degree slope, meaning you multiply your 1-mile horizontal distance by 1.064 for an actual hiking distance of just less than 1.1 miles.
Slope Slope angle Map miles
percentage (degrees) times
36% 20 degrees 1.064
58% 30 degrees 1.155
83% 40 degrees 1.31
100% 45 degrees 1.41
120% 50 degrees 1.56