 The next issue is that exemplified properties are rarely exactly imputed onto target systems. According to  Representation-As  the imputed properties are either the ones exemplified by the \(Z\)-representation, “or related ones”. Frigg and Nguyen (2016: 228), building on Frigg (2010a: 125–135), prefer to be explicit about the relationship between the exemplified properties and the ones to be imputed onto the target. They do this by introducing a “key”, which explicitly associates the exemplified properties with properties to be imputed onto the target. For example, in the case of a London Tube map, the key associates particular colours with particular tube lines, and in the case of idealisations the key associates de-idealised properties with model-properties.