The pattern is irregular because the height of the shape changes each time it is repeated. View of the Whirlpools at Awa, from an untitled set of three triptychs, Utagawa Hiroshige, 1857 ...

In Echelonnement (1934), Sophie Taeuber-Arp has taken a simple white shape as her motif and repeated it against a blue background. The pattern is irregular because the height of the shape changes ...