For some reasons there are many combinations of circles, rings, lines and pathways that are very rare or even non-existent in the formations.

Rare or non-existent combinations

Why do the Circle makers very rarely make closed rectangles or polygons? I think the answer lies in the restrictions of the Brush this time. The plasma ball can't make sudden sharp turns - it's simply against the rules of nature. You can make ring shaped tracks on the ground with a motor cycle, but not squares (not that a motor cycle is all that natural...)!

Update: Rectangles have appeared a few time since 1999.

A rectangle can't be made like a circle: running the Brush a spiral path. It must be made by several linear "sweeps". If one Brush makes a stroke 50 cm wide, it means that the creation of a 10 x 10 m square would take 20 (!) sweeps. This could be done by a single Brush that goes round a large ring (at least some 30 m in diameter) and sweeps the region defined by linear G- and C-barriers 20 times. Or it could be done by several Brushes. Anyway, with the same effort maybe 10 circles or rings could be made. So it is only understandable that rectangles or polygons are not the Circle Makers favourites!

An example of another rare shape is the shape of a "racing track" (see pattern 2 above). I think the problem with this is that the circular and linear barriers need to be extremely precisely positioned so that they align. Also we must remember that the linear barriers are not lines with clear beginnings and endings (I will later demonstrate with images why these shapes are difficult to create).

It is also obvious that the way how the circles and lines are organized follows some laws of mathematics. Typically the circles are positioned in relation to each other following amazing geometrical logic! Perhaps the most common combination of circles is when six circles of the same size are positioned on the perimeter of a seventh circle with regular intervals. This combination is called "the seed of life". By "painting" different segments of the intersecting circles it's possible to make very many different patterns using just this combination of seven circles.