Computation
In the simplest case of a trip where hikers only travel up on their way to a single summit, the cumulative elevation gain is simply given by the difference in the summit elevation and the starting elevation. For example, if one were to start hiking at a trailhead with elevation 1,000 feet (300 m), and hike up to a summit of 5,000 feet (1,500 m), the cumulative elevation gain would just be 5000 ft - 1000 ft = 4000 ft. The loss of elevation on the descent is not relevant, because only increases in elevation are considered in this measure.
However, when climbing a mountain with some "ups-and-downs", or traversing several mountains, you must take into account every "up" along the whole route. This even means that the (usually small) uphills on the descent must be counted. For example, consider a mountain whose summit was 5,000 feet (1,500 m) in elevation, but somewhere on the way up, the trail went back down 250 feet (76 m). If starting at an elevation of 1,000 feet (300 m), one would gain 4,250 feet (1,300 m) on the way up (not 4000, because 250 is lost and has to be "regained") and 250 more feet on the way down, leading to a cumulative elevation gain of 4,500 feet (1,400 m) on the trip.
If one were to hike over five hills of 100 vertical feet each, and back, the cumulative elevation gain would be 5 x (100 ft) x 2 = 1000 ft.
This concept makes travel on mountains which have more "ups-and-downs", or are generally more rugged, significantly more strenuous.
Read more about this topic: Cumulative Elevation Gain
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