1. A method of processing data in a tile based rendering system, wherein the method comprises a geometry processing phase and a rasterisation phase, wherein the geometry processing phase comprises the steps of: retrieving position data of primitives stored in a memory; transforming the retrieved position data to screen space; and using the screen space position data to generate, for each of a plurality of tiles of the tile based rendering system, a list of pointers to primitives in the memory which when transformed are at least partially in the respective tile; and wherein the rasterisation phase comprises the steps of: for each of the tiles, retrieving pointers from the respective list; retrieving data of primitives from the memory corresponding to the retrieved pointers of each list; transforming the retrieved data of primitives to screen space; and rendering the primitives.