A note about methodology: when using a topographic map to determine prominence, one often has to estimate the height of the key col (and sometimes, the height of the peak as well) based on the contour lines. Assume for simplicity that only the col elevation is uncertain. There are three simple choices. The pessimistic, or clean prominence, assumes that the col is as high as it can be, i.e., its elevation is that of the higher contour line nearest the saddle. This gives a lower bound on the possible prominence of the peak, ignoring map error; inaccuracies in mapping lead to further uncertainties and a larger error bound. Optimistic prominence assumes that the col is as low as possible, yielding an upper bound value for the prominence. Midrange or mean prominence uses the mean of these two values. Mean prominence is sometimes referred to as rise. In Britain, where topographic mapping is more detailed than in many countries, it is customary to use a fourth method: interpolated prominence. The true prominence is estimated by visualising the three dimensional surface in the neighborhood of the col and interpolating between the enclosing contours.