Hunter, AndrewWillis, Philip2014-10-212014-10-2119911467-8659https://doi.org/10.1111/1467-8659.1020097Many quad encoding technique have been published previously, using a variety of approaches to the different facets of quad storage, representation and manipulation. We review the major classes and identify three parameters which distinguish them. These are then used explicitly to classify a large number of published methods, with short discussion on each. In doing this we are also able to highlight some new approaches, to identify rare examples which escape the classification, and to suggest approaches to choosing a method to suit a given application.10.1111/1467-8659.102009797-112