The slope and shape of the nested species–area relationship (SAR) can be derived using geometrical considerations. The local slope of the nested SAR is determined by mean species occupancy at a given scale. Thus, any factor that affects the scale dependent occupancy patterns of individual species will affect the overall shape of the nested SAR. Using only geometric considerations, we can derive not only the formula relating mean occupancy to the overall nested SAR slope, but also the overall triphasic shape of the nested SAR. The relatively shallow slope of the nested SAR at intermediate spatial scales, which can be well approximated by a power law, can be attributed to the scale independent (approximately fractal) spatial distribution of individual species. The shape and slope of the nested SAR are linked to beta diversity patterns as well as to the species abundance distribution (SAD), although we argue that the SAD is in fact a derived pattern which cannot be used to construct the nested SAR. In general, geometrical considerations provide a first-order explanation of the nested SAR, while biological factors affect the basic parameters of species distributions and thus act to determine the specific nested SAR in any given case.