From these criteria 13 types of world agriculture were derived (Map 1.5; Table 1.10). These are essentially generalized edscriptions, but they have been utilized for various purposes and usually with little modification (e.g. Symons, 1968). Never-theless, suggestions have been made regarding the addition of more specific criteria that can be measured quantitatively (Helburn, 1957). It is the lack of available data and the complexity such criteria would create that has contributed to its lack of application (see Evans, 1996, for limitations of the UK’s agricultural census).