A scene to be rendered is divided into plural individual sub-regions or tiles. The individual sub-regions 51 are also grouped into differing groups of sets of plural sub-regions. There is a top level layer comprising a set of 8×8 sub-regions which encompasses the entire scene area. There is then a group of four 4×4 sets of sub-regions, then a group of sixteen 2×2 sets of sub-regions, and finally a layer comprising the 64 single sub-regions. A primitive list building processor takes each primitive in turn, determines a location for that primitive, compares the primitive's location with the locations of the sub-regions and the locations of the sets of sub-regions, and allocates the primitive to respective primitive lists for the sub-regions and sets of sub-regions accordingly.