Guy/N7UN summarized it as follows:
From Wikipedia: Topographic Prominence
There is always a lot of confusion with the general public around a summit “being prominent vs having prominence“.
In the US, the FCC uses HAAT (Height Above Average Terrain) as a metric for determining how prominent a transmitting site antenna will be versus the surrounding (out to 16 km) landscape.
Whereas topographic prominence characterizes the height of a mountain or hill’s summit by the vertical distance between it and the lowest contour line.
It is used in mountaineering and by cartographers. SOTA uses this metric as as an “objective measurement that is strongly correlated with the subjective significance of a summit.”
Fortunately, the data-sets used for the NA SOTA summit lists has it’s origins with the USGS and the NED National Elevation Dataset.
So the prominence is both a measured (was land survey but now mostly by satellites) and a calculated metric. So the USA (Alaska is currently being studied/calculated) benefits from this dataset metric. To determine this metric manually and from maps would be a daunting task which is the challenge for SOTA in Canada and Mexico.