## 3 Methodology  
### The Appropriate Assessment Procedure under the Habitats Directive  
We discuss the AA of the municipal master plans of Sardinia on the basis of the provisions of the Methodological Guidance (MG) quoted above [6]. The MG is essentially related to Articles 6.3 and 6.4 of the Habitats Directive. The methodology for the AA implementation is described in the third section of the MG, even though only paragraph 2 defines the assessment phases, while the others concern the screening procedure (paragraph 1), the issues of alternatives to the proposed plan or project that might possibly generate negative impacts on a Natura 2000 site (paragraph 3) and of how to deal with situations characterized by lack of alternative solutions and important negative impacts (paragraph 4). The AA of a municipal master plan (MMPs) on the Natura 2000 site(s) located in the area ruled by the municipal administration (\"Site\" hereafter) is based on an information set related to the Site and to the rules of the MMPs concerning the municipal area that overlaps the Site (Site overlapping area, SOVLA). According to the MG, a Site can be characterized through the following information set: (i) habitats; (ii) species; (iii) conservation objectives; (iv) ecological requirements; (v) threats, pressures and activities with impacts on the Site; and (vi) relevant conservation issues. This set contains information which, on the one hand, comes from the characterization of habitats, species and impacts contained in the Site's Natura 2000 Standard Data Forms (SDFs) available, for each Site, on the Internet site of the European Environment Agency concerning the Natura 2000 network [28,29]. On the other hand, supplemental information is required, which is related to conservation objectives, ecological requirements and relevant conservation issues. This information can be collected from several sources, such as scientific studies concerning site-specific historical, natural and environmental issues, on-sitesurveys related to the conditions of habitats and species and on the local factors, which may generate negative impacts, _etc._  
The SDFs contain detailed information on habitats and species, in compliance with the classification of the Habitats Directive. This includes habitats' and species' interpretation and representation elements. Habitats are classified into natural habitat types of community interest and priority natural habitat types [30]. Species of community interest are drawn from those listed in [31]. The informative content of the SDFs concerning habitats and species is defined as follows [32]. Information concerning interpretation and representation of habitats includes:  
* representativity, that is Criterion A. (a) of Annex III of the Habitats Directive: the representativity of an habitat for a Site is related to how a habitat is typical for the Site, and either for groups or for combinations of groups of habitats; the assessment of representativity should be implemented taking account of the provisions of the Interpretation Manual issued by the DG Environment of the European Commission [33];
* relative surface, that is the ratio of the area of the habitat in the Site to the total area covered by that habitat type within the national territory; that is, Criterion A. (b) of Annex III;
* state of conservation in terms of structure and functions and restoration possibilities, that is Criterion A. (c) of Annex III;
* global assessment of the habitats, with reference to the three criteria indicated above, that is Criterion A. (d) of Annex III. Information concerning the interpretation and representation of species includes:  
* population of the species in terms of the ratio of the number of individuals with respect to the total population within the national territory, that is Criterion B.