[en] Since the Earth Summit in Rio, declining biodiversity has become a subject of general concern for many countries. To counter these negative trends, government nature policies in Europe at least are now thought out primarily in terms of networks. They concern new areas outside nature reserves, new players and new management strategies. Consequently, these policies should themselves become the subject of new public debate. Our study concerns the analysis of the forms used to collect the data required to set up the European Union's Natura 2000 network and maps drawn as part of the Council of Europe's Pan-European Ecological Network strategy. The aim of this article, which takes the perspective developed by the sociology of science, will be to show how the forms and maps used in these new nature policies produce knowledge that precedes policy discussions to search for the best possible socio-political compromises. In other words, the knowledge that is collected in and by means of these documents, forms and maps offers a cognitive way of framing the subsequent public debates.