This paper presents the first theoretical study of spatial genetic structure within nonuniformly distributed continuous plant populations. A novel individual-based model of isolation by distance was constructed to simulate genetic evolution within such populations. We found larger values of spatial genetic autocorrelations in highly clumped populations than in uniformly distributed populations. Most of this differencc was caused by differences in mean dispersal distances, but aggregation probably also produced a slight increase in spatial genetic structure. Using an appropriate level of approximation of the continuous distribution of individuals in space, we assessed the potential effects of density, seed and pollen dispersal, generation overlapping, and overdominance selection at an independent locus, on fine-scale genetic structure, by varying them separately in a few particular cases with extreme clumping. When selfing was allowed, all these input variables influenced both aggregation and spatial genetic structure. Most variations in spatial genetic structure were closely linked to variations in clumping and/or local density. When selfing was not allowed, spatial genetic structure was lower in most cases.