The rule based system for Annex I habitats is designed to promote their consistent identification between Member States. A direct key is not possible because the list of Annex I habitats has been produced by national experts over the years and requires scientific judgement in many cases.
The structure of the system is first to identify Annex I habitats that are landscape units or habitat complexes and then to use the General Habitat Categories (GHCs) (Bunce et al., 2008, 2011) as a framework to identify other habitats. All Annex I habitats are characterised by some summary data. The full information for the identification of the Annex I habitats is given in the Interpretation Manual of EU27, together with additional information from Evans (2010).