The classification of geometric decorative motifs has tended to emphasise the geometric by comparing the decoration to mathematically perfect constructions. Focussing on spirals as exemplars, this paper proposes that additional information may be gleaned from historic decoration on the assumption that such decoration often does not conform exactly to mathematically correct constructions. Shape-matching analysis methods combined with the analysis of stylistic variables are put forward as a means of comparing cultures; in particular, of looking for evidence of cultural diffusion and studying the manner and rate of evolution of geometric motifs.