Rim-to-rim diameter (D). Value is actually diameter of a circle with an area
equivalent to the crater's. I measured the area digitally by outlining the rim
and counting the number of enclosed pixels. For craters with terracing, the rim
is defined by the outermost boundary of the observable terraces. Most previous
studies on other planets were made with photographic products rather than
digital data, and typically involved measuring diameter using a set of
rim-to-rim measurements or by fitting circle templates to the craters. In most
cases the end result is nearly the same. Error is ± 2%. For crater fields, the
equivalent single crater diameter (SD) entry of the multiple impacts database
is used for D.