Understanding high-temperature superconductivity is a major aim of condensed-matter science, which is of fundamental importance and may ultimately allow the design of materials with higher superconducting temperatures. In the superconducting state and its precursor "pseudo-gap" state, magnetic moments (spins) do not form a conventionally-ordered structure. However, they are locally strongly correlated, and these local correlations may be important for superconductivity. We propose to use a combination of neutron total-scattering experiments and atomistic refinement techniques to map the nano-scale spin arrangements in the canonical high-temperature superconductor YBa2Cu3O{6+x} (YBCO). The main aims of proposal are to determine the length-scale of spin correlations, the magnitude and nature of their anisotropy, and whether they show a liquid-crystal-like (nematic) ordering.