The approval of genetically modified organisms [GMO] for deliberate release and placing on the market requires GMO environmental risk assessment [ERA] and GMO environmental monitoring [EM]. Both GMO ERA and GMO EM are still under discussion. The goal of this article is, firstly, to analyse principles of GMO EM as published in the Association of German Engineers [VDI] Guideline 4330 Part 1, focusing on the characterisation of the receiving environment affected by GMO cultivation and the

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... ativeness of GMO EM to assess large-scale implications of GMO cultivation. Secondly, the article introduces measures to meet these issues by the use of map data and statistics within a geographical information system [GIS]. Finally, three case studies exemplify the application of data and methods. To deal with spatial issues of GMO EM as outlined in the VDI Guideline 4330 Part 1, a GIS-based approach is presented. It relies on both spatial data collected from several sources which were derived from sample point data and geostatistical and multivariate statistical methods within a GIS environment. Data used for describing the receiving environment and for planning and evaluating monitoring schemes comprise information about land use, climate, phenology, soil coverage, species distribution and ecoregions. The case studies deal with (1) ecological land classification for characterisation of GMO-receiving environments and representative EM, (2) selection of representative sites for modelling GMO dispersal, and (3) delineation and mapping of segregation distances. Even a systematic and stepwise-structured risk assessment cannot cover all risk relevant questions, especially large-scale, long-term and combinatory effects which may not occur before the conventional application of the respective GMO. Hence, GMO EM is crucial to deal with unanticipated and undesirable effects. The article gives an overview of a GIS implementation and relevant geodata promoting GMO EM.