Central structure diameter (Cd). Value is actually diameter of a circle with an
area equivalent to that encompassing any central structure; measured in the
same manner as rim-to-rim diameter. Previous studies have measured peak ring
diameter by fitting a circle to the peaks of the ring massif (e.g., Pike and
Spudis 1987, EM &P, v. 39, 129). For the sake of interplanetary comparisons in
the text we also used this older technique to measure peak ring diameters for
single- and double-ring basins. Peak ring diameters using this second technique
is in the separate sheet. Error for central peak or peak ring diameter using
the equivalent area technique is ± 6%. Error for peak ring diameter using the
circle-fitting technique is ± 1.7 km.