are not taken into account. If they were, the key col would be along the 26 m Gaillard Cut and Denali would have a prominence of 6,168 m. While it is natural for Aconcagua to be the parent of Denali, since Denali is a major peak, consider the following situation: Peak A is a small hill on the coast of Alaska, with elevation 100 m and key col 50 m. Then the encirclement parent of Peak A is also Aconcagua, even though there will be many peaks closer to Peak A which are much higher and more prominent than Peak A (for example, Denali). This illustrates the disadvantage in using the encirclement parent. Mount Whitney (4421 m) has its key col away in New Mexico at 1347 m on the Continental Divide. Its encirclement parent is Pico de Orizaba (5,636 m), the highest mountain in Mexico. Orizaba's key col is back along the Divide, in British Columbia. The key col for Mount Mitchell, the highest peak of the Appalachians, is in Chicago, the low point on the divide between the St. Lawrence and Mississippi River watersheds. A hill in a low-lying area like the Netherlands will often be a direct child of Mount Everest, with its prominence about the same as its height and its key col placed at or near the foot of the hill, well below, for instance, the 113-meter-high key col of Mont Blanc. Calculations and mathematics When the key col for a peak is close to the peak itself, prominence is easily computed by hand using a topographic map. However, when the key col is far away, or when one wants to calculate the prominence of many peaks at once, software can apply Surface Network Modeling to a digital elevation model to find exact or approximate key cols. Since topographic maps typically show elevation using contour lines, the exact elevation is typically bounded by an upper and lower contour, and not specified exactly. Prominence calculations may use the high contour, giving in a pessimistic estimate, the low contour, giving an optimistic estimate, their mean, giving a "midrange" or "rise" prominence, or an interpolated value, customary in Britain. The choice of method depends largely on the preference of the author and historical precedent. Pessimistic prominence, and sometimes optimistic prominence, were for many years used in US and international lists, but mean prominence is becoming preferred. Wet prominence