This Joseph Rowntree Foundation study by researchers from the Universities of York and Durham charts the rapid growth of internet-based neighbourhood information systems (IBNIS) that are making publicly available ever more detailed neighbourhood information. Based on interviews with site developers in the UK and USA the research looks at how technology can be used to classify and sort people and places. The study found that IBNIS have the potential to fundamentally change or solidify the image of individual neighbourhoods with real consequences for people on the ground. Raises concerns that taken as a whole IBNIS such as www.upmystreet.com could encourage social sorting. IBNIS can have a strong influence on the intensifying processes of social differentiation and fragmentation. Concludes that site developers and policy makers should co-operate to put into place a framework to minimise any damaging outcomes from IBNIS.