Consider the Hexagon. It is a naturally occurring shape in a spherical world.
There is no mystery here.
When you take round objects of the same size and pack them together the first feature that forms is a hexagon.
That brings us to the principle reason for this observation.
Look at certain planetary features and the angle that forms in some hip ridges of a peak. If EDM is involved in the carving of material away from the surface, leaving only the peak, then three hip-ridges might form because when three craters are adjacent to one-another the angle formed is 120 degrees and that is a three legged spider. This is the first indication of a non-random process at work.
Hexagonal craters might form as the force being applied must obey the influence of other forces adjacent to that location. In the case of those on Mars,, the ground underneath may be more magnetized than other areas..
Look at the pictures in this sub-directory to see how an electrostatic field, in close proximity to a plasma ball, causes the filaments to arrange themselves in groups and also establish hexagonal boundaries.
Inset image is of Saturn's polar hexagonal feature. (credit: Nasa, JPL, Casini and all)
An arc interacting with a surface leaves a polarity signature on that area of the surface, and to that surface, material will accumulate according to that signature by electrostatic redistribution of material. Additionally the arc might erode away material leaving some material behind. When deposition is involved, just the area between the three point of discharge welcome redeposition as seen in the image below.
See a planetary version of EDM through zunil's Ring of craters
Update August 2014
Do Take a moment to view the ideas presented in this video released
in 2013 by David LaPoint..
Then compare the results from a CRT experiment with a plasma ball in close proximity.
The motivation behind my experiment was related to crater
features and Saturn's polar polygonal anomoly,,
but there was more to be gleened from that moment of inspiration, than actually occurred.