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.