1. A method of sorting graphics primitives for rendering into lists representing different areas of a render target to be generated in a tile-based graphics processing system, the method comprising: dividing by processing circuitry a render target into plural rendering tiles for rendering purposes; preparing by processing circuitry primitive lists indicating primitives to be processed for at least two different sets of sub-regions of the render target area, at least one of the two different sets of sub-regions of the render target area comprising sub-regions of the render target area that are bigger than a single rendering tile; the method further comprising: for a primitive to be rendered: determining by processing circuitry sub-regions of at least two of the at least two different sets of sub-regions of the render target area that the primitive could need to be listed for in order to render the primitive; using a cost function by the processing circuitry to determine plural cost values representing the cost of listing the primitive in the primitive lists for the render target area sub-regions that it has been determined that the primitive could need to be listed for; and selecting by the processing circuitry which of the render target area sub-regions that it has been determined that the primitive could need to be listed for in order to render the primitive to list the primitive for based on the determined plural cost values, and including the primitive in the primitive lists of those selected sub-regions by the processing circuitry.