Summit Analysis using the National Elevation Dataset
Steepness by Fixed Drop
Steepness Measurement Methods: Fixed Drop versus Fixed Distance.
Existing steepness calculations found at ned-files.com measure vertical drop within a fixed horizontal distance. A new calculation measures average horizonal distance(in all directions) to a fixed vertical drop. The two approaches are related, but can yield slightly different results.
Peak with relatively small, flat tables atop steep surrounding slopes do much better using fixed drop vs. fixed distance. The prime example is Longs Peak which grades out much steeper using fixed drop, as the method captures some of the steep slopes which are not close enough to the actual summit be included in the 100m fixed distance calculations. Snowdon Peak is another good "table top" example.
Peaks with flat terrain to one side but very steep drops on the other(think canyon rim summits) sometimes get high marks using the fixed distance method but get exposed as overall steepness imposters using fixed drop. Ogallala Peak is an obvious case. Fixed distance gives significant weight to sheer cliffs to its east and doesn't entirely penalize for the expansive, gradual sloping terrain to the west. The fixed drop method takes the huge flat area fully into account, and correctly shows it to be a less steep peak overall compared to what fixed distance suggests.
Other peaks which get docked using the fixed drop method are those having vertical drops near the highest point which are less than the pre-set drop amount used in the fixed drop calculations. An example is UN 13017. Theere is obviously near-vertical rock faces near the summit, but the vertical drops are only around 200'. Fixed drop can recognize that the steep drops near the summit are really not all that large of a vertical distance and won't overrate steepness in the way that fixed distance can do in certain instances such as this.
For the CO 13ers list linked below, the drop is set at 300'. To prevent skewed results due to outliers, the drop cannot be greater than a peak's prominence, thus only ranked 13ers are included. Click on the average distance figure for a map showing the drop area. The actual drop area amount correlates well with average distance figure, but not exactly.
Looking at the 13ers list, the resultant ranking of the peaks based on the two methods is very similar. The fixed distance method, particualrly at 100m, is still preferred for finding potential technical peaks and summits which have the steepest terrain right near the highest point. Fixed drop does not pick out these types of peaks quite as well, but does offer corrections to peaks which, due to the special circumstances mentioned above, score too high or too low using fixed distance.