  Elevation has long been the standard for quantifying the relief of mountains
and other landforms on Earth and beyond. Nevertheless, elevation has its
limitations. By itself, a location's elevation reveals little about its
vertical position relative to its surroundings, especially for seabed and
extraterrestrial features. Furthermore, on planets and asteroids without a sea
level, the zero-elevation datum is defined rather arbitrarily, making elevation
values rather meaningless without also considering relative elevation
differences. In light of these factors, this paper introduces new topographic
measures based purely on gravity and the actual planetary surface, rather than
on an arbitrary datum. Unlike elevation, the so-called datumless measures --
with the names of dominance, jut, submission, and rut -- each describe a
different aspect about a location's vertical position relative to its
surroundings. They can be used to objectively compare the relief of mountains
and other landforms, including across different planets. The datumless measures
may be of interest to planetary scientists seeking universally standardized
measures of relief, Earth scientists seeking to correlate geomorphological
properties with natural phenomena, as well as mountaineers and hobbyists
seeking new ways to describe the wondrous landscapes of this universe.
