- at least five points, because three points would be perceived as a triangle and four as a square;
- the points, and track of any curve, to be equally distant from a central point in space; and
- they would have to close enough to each other to provide perceptual closure.
Naturally-occurring circles include bubbles, the sun, the moon, and organisms featuring radial growth.
Ellipses, often interpreted as circles viewed at an angle, possess the same properties i.e. feeling of enclosure, and direction of attention inward to a focal point. Unlike a circle, ellipses have only two axes of symmetry and they have greater dynamism because the speed of visual flow changes - accelerating or decelerating - along its periphery.