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Next  Deren Li professor LIESMARS, Wuhan University, Wuhan, China dli@wtusm.edu.cn Huayi Wu LIESMARS, Wuhan University, Wuhan, China wuhuayi@mail.liesmars.wtusm.edu.cn As a part of Digital Earth, the core of Digital China is SDI of the country and that of all levels of administrative regions. This paper discusses in detail the requirement of GIS software system for the construction of SDIs of China Despite the nature of globalization of the information revolution, most policies for information and telecommunications infrastructure are developed and working at the national level. These national policies reflect regional economic, social, historical, and political circumstances. Based on a dozen case studies analyzing how national-level policy initiatives address the challenge of information technology, interactive content, and new applications, the former US President, Bill Clinton, proposed the concept of ‘Information Highway’ and issued the National Information Infrastructure (NII) Initiative in 1993. This Initiative clearly concluded that an advanced communications and information infrastructure should be a national priority of the US. This is the first proposed national information infrastructure in the world. However, the economic, social and environmental development of the world is based on the use of land, water and other natural resources. Major activities of human being such as mining, farming, forestry, transport, tourism, coastal zone management and community services are directly operating on earth surface. It is well accepted that more than 80 per cent of the information we are concerned with is spatial and geographical. So, the National Spatial Data Infrastructure is the core and foundation of NII. Consequently, in 1994 the Executive Order 12906 was issued for creating the US NSDI in order to further accelerate spatial data sharing and standardization. The concept of NSDI was in later years further extended to Global SDI (GSDI) and regional SDI. All these SDIs will provide a unified way to access geographic information at various levels by developing an online directory and distributed clearinghouse with consistent standards and policies for data sharing. A conceptual breakthrough related to GSDI is Digital Earth (DE) proposed by the former US Vice President Al Gore in 1998. Al Gore described the DE as virtual representation of our planet that enables a person to explore and interact with the vast amounts of natural and cultural information gathered about the Earth. It's obvious that GSDI is the mathematical base and spatial information framework of DE. As the first step of creating the DE, a lot of countries have started to develop NSDI and/or regional SDIs in recent years. China has also worked on all aspects to create a country-level SDI and different levels of regional SDIs. Based on these National SDI and SDIs, all related information including natural, cultural, social, economical and historical information is integrated, fused and utilized through this platform to form digital city, digital province and Digital China. TECHNOLOGICAL REQUIREMENTS FOR SDI The ability of integrating multi-source massive data into a seamless database With the development of earth observation and data collection technologies, geo-spatial data has been in intensive explosion. Terabytes of data are generated from different programs everyday. A national SDI is required to carry massive multi-source data in a distributed computing environment. And, SDI is also required to take in the growing dataset and have the ability to update data. Object-oriented and flexible architecture Object-Oriented theory and programming provide a powerful way of modelling the structure of information in SDI. The mechanism of abstraction, inheritance and polymorphism makes an object-oriented GIS capable of protecting private information as well as opening public methods of geographical objects in SDI. More over, by object-oriented modelling, it is very easy to map the digital object to the real object of the world and to understand the behaviours of queries and analysis for various users. A GIS platform for SDI development should be in flexible architecture, extensible and easy for customisation. Multi-dimensional and real-time 3D visualization SDI is a platform providing geographical information. It also has to provide ‘user interface’ for various users to view the information. As DEM and 3D models are fundamental information in SDI, ready-to-use 2D display or 3D rendering tools are essential for GIS software for SDI. As is described in Al Gore's speech, users can view the earth from the space and zoom into a city, even a building. If the network bandwidth is broad enough in future, some real-time information such as running cars can be also viewed through the platform. So, SDI should have the capacity of integrating dynamic information.
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