Technological development and increasing awareness of geodata and its use has caused an explosion of digital content. However, this was not accompanied by dissemination and accessibility measures. Spatial Data Infrastructures (SDIs), allowing extensive reuse of geoinformation, may offer a solution. SDIs face organisational, technological, legal, cultural and linguistic challenges. The enrichment of geodata by semantically well-defined metadata and widespread implementation of SDIs, as foreseen

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... y INSPIRE, could help to overcome these difficulties. The European thematic network eSDI-Net+, co-funded by the EC, aims at bringing together existing SDI key players and target users to facilitate exchange of experiences and best practices at sub-national level. Therefore the project developed a SDI assessment methodology and framework. It identified about 200 working, accessible and intelligible SDI solutions and selected 12 best practices. The next step is to transfer these experiences back to local communities and to disseminate them among the global GI community worldwide. Keywords: Digital Earth, Spatial Data Infrastructures (SDIs), sustainable development at local and regional levels, SDI Best Practices in Europe, SDI assessment, cross-border dialogue, transfer and exchange of experiences KEY DEVELOPMENTS TOWARDS DIGITAL EARTH IN THE SDI FIELD In the last 20 years many of initiatives aimed at increasing the availability and accessibility of geographic information. Development of spatial data infrastructures (SDIs) was one of the major steps in organising geographic information towards the vision of Digital Earth. By the mid 1990s, Masser (1999) identified about 11 SDIs at varying stages of development spanning large countries like the USA, Canada, and Australia, small ones like the Netherlands and Portugal, and developing nations like Malaysia, Indonesia, and Qatar. This first generation of SDIs was mainly led by national mapping agencies and oriented towards the completion of national spatial databases addressing topography and further key layers of general use. The documentation of existing resources via metadata, and access mechanisms through catalogues and clearinghouses were additional key features of these early developments. Since then the SDI field has been transformed by two significant developments. The first of these is the accelerated diffusion of SDIs throughout the world during the last ten years. As a result, most countries in Europe have now taken steps to implement at least one component of a national SDI. This development was facilitated by the establishment of the Global Spatial Data Infrastructures Association in 1996, which has helped the promotion of best practice and sharing of experiences, and capacity building in the Americas, Africa, Asia and the Pacific and Europe. In Europe, in the year 2007, an important development was the adoption of a legal framework to establish a distributed Infrastructure for Spatial Information in Europe (INSPIRE) built on the SDIs of the 27 Member States of the European Union. INSPIRE was one of the answers to the many challenges identified in the 6 th European Environmental Programme like clean air, soil protection, waste prevention and other (Brepoels 2009). Developing a common policy to face these challenges required the availability of reliable and high-quality spatial information. Before INSPIRE, this was a difficult task due to a very restrictive data policy of the EU Member States which hindered the exchange of data and information. Furthermore, there was a lack of common standards, which made the data not comparable. Since the INSPIRE initiative entered into force in May 2007, a lot has been accomplished. Regarding the SDI field, the INSPIRE initiative has played an important role in promoting the SDI diffusion process in Europe. Similar developments have taken place throughout the whole world. 3 rd ISDE DIGITAL EARTH SUMMIT 12-14 June, 2010, Nessebar, Bulgaria At the international level, the United Nations Geographical Information Working Group (UNGIWG), being a network of professionals working in the fields of cartography and geographic information science, made a major contribution to build the UN Spatial Data Infrastructure needed to achieve sustainable development. It was formed in 2000 to address common geospatial issues -maps, boundaries, data exchange, standards -that affect the work of UN Organisations and Member States. In 2006 the UNGIWG developed the vision, strategy and the institutional governance framework for a United Nations SDI initiative, allowing involvement of non-UN partners. The nature of the second SDI generation has shifted with an increased number of stakeholder organisations involved in the process, focusing on distributed data and processes, and the interoperability of services to discover, view, access, and integrate spatial information. The interoperability of systems through services was addressed by the Open Geospatial Consortium established in 1994 as an international partnership between government agencies, industry, and academia. The OGC client-server interface specifications and the standards adopted by the International Standards Organization (ISO) have become the cornerstone of most existing SDIs. Despite this emphasis on interoperability through services, the underlying basic approach to a SDI architecture has not evolved much during the last 10 years.