1. A computer system comprising: a layer contained within a virtual environment holding templates for generation of one or more other layers within the virtual environment; generating said one or more other layers; interacting with said one or more other layers by one or more users resulting in at least one alteration to the said other layers; and determining, by reference to permissions data, whether the at least one alteration should be made persistent with regard to the one or more other layers, or the one or more users.