Following the Educational Reform Act of 1988, families in England and Wales have been free to identify a preferred school for their children’s secondary education. However, as part of this open selection, the demand from parents opting to send their children to the best performing schools far outstrips the supply of available places at them, and consequently many schools ration places using entry criteria that favour those pupils domiciled close to the school. Through this geographic selection process, choice is spatially sorted and access to the best schools is often crucially dependent upon where parents live. After illustrating this problem, this paper develops an automated modelling technique that can be used to define and map school catchment areas based on the home locations of pupils attending every publically funded school in England. It then develops this framework to create a web based decision support tool to aid parents seeking secondary school places.