| Distributed GIS is an inevitable trend of GIS today. Distributed GIS is now encountering with many severe challenges. However, existing solutions for DGIS still have many limits and their capabilities need to be enhanced.This dissertation focuses on how to implement a distributed geographic information system (DGIS) based on the web, and how to construct the model of distributed geographic information system, which solves not only the problem of GIS data sharing but also the problem of further GIS processing capability services.Geographic information is the basis of the GIS. The research on expression and management of geographic information is implemented by the research on geographic spatial data model. In more sense, it's the symbol of GIS development level. Distributed geographic information is analyzed and data model of geographic spatial information is proposed. In addition, such related problems as component GIS and WebGIS technology are elaborated.Fast navigation to distributed geographical spatial data has been the keystone of distributed GIS. Analyzing origin, concept, function, status , standa,. content and expression of the metadata, the concept of the geographic spatial metadata is proposed, and GIS data interoperability & GIS processing interoperability are elaborated in chapter 3. According to different emphasis, GIS interoperability is divided into three sorts, that is, data interoperability (technology interoperability) , processing interoperability(services interoperability) and semantic interoperability. At present, the research on GIS interoperability is more emphasized on GIS data interoperability. However, the research on processing interoperability and semantic interoperability are so far as mature. Hence, a distributed and network-based geographic spatial metadata database framework is presented.In chapter 4, on the basis of analyzing distributed GIS services, the general concept model and the model of distributed GIS services based on Java technology are proposed. Geographic Information Services, also called GIS Services, mean geographic information and geographic information processing services.GIS services are most appeared in the form of service chaining. Cited with some basic services, three kinds of DGIS service chaining-user defined service chaining ^static chaining and workflow-managed service chaining-are proposed and elaborated. Some new concepts such as component registration and component meta-information are introduced. The registration model of distributed geographic component, a very important part of the service model, is proposed.Since DGIS service system is a very complex system, a prototype implementation based on Java technologies has been developed. The prototype system just offers some basic service components, such as registration component, SRS projection component, web mapping component and address matching component. Finally, we employ multi-threaded technology to implement a prototype system, which is based on Java, and perform an analog application in city plan and management. The model of GIS services can apply to many fields such as government, military, enterprise and individual users. Therefore, it has a nice application prospect.Practice shows that our prototype system has potential good capabilities. Because of the limits of system design and implementation technology and further development of GIS technology, there is a long way for this system to apply in the practice. It is also one of emphases of our next work.Distributed GIS is a brand-new field in which it not only gives a great impact on traditional conception and technology but also further affects the development of GIS methodology, geographical information industry and Digital Earth. Since the research on this domain is immature, it is elementarily discussed on the model of distributed geographic information system and related problems in this dissertation. It is unavoidable to have oversights and partials in this dissertation. So criticisms on these faults will be welcomed and grea...
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