We investigated the dewetting process on flat and chemically patterned surfaces of ultrathin films (thickness between 2 and 15 nm) of a cylinder forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) spin coated on poly(styrene-r-methyl methacrylate) random copolymers (RCPs). When the PS-b-PMMA film dewets on a 2 nm-thick RCP layer, the ordering of the hexagonally packed PMMA cylinders in the dewetted structures extends over distances far exceeding the correlation length obtained in continuous block copolymer (BCP) films. As a result, micrometer-sized circular droplets featuring defectless single grains of self-assembled PS-b-PMMA with PMMA cylinders perpendicularly oriented with respect to the substrate are generated and randomly distributed on the substrate. Additionally, alignment of the droplets along micrometric lines was achieved by performing the dewetting process on large-scale …