Curve

Smartphone app icons are not rounded squares — they are "squircles," a portmanteau of square and circle. Defined by the mathematical equation |x|⁴ + |y|⁴ = r⁴, this superellipse shape gives a smoother, more pleasing impression than simply rounding the corners.

Highway and railroad curves are not circular arcs — they use a special shape called a "clothoid" (Euler spiral). Its curvature changes gradually, so centrifugal force increases smoothly when transitioning from a straight section to a curve, rather than hitting suddenly.