| The Informatization and the globalization of economy have become a general trend of the social development. Informatization has become an important indicator of comprehensive strength and development of a nation, region or a city social economy. A city, being of the center of economy, culture, information and policy, is the source and settlement of civilization, so the informatization of a city should be an essential component of global informatization. The Digital City, being another leap of realization the material city by human, is a important support of the healthy, sustainable development of the urban, social, economic, population. When the concept of Digital City comes into being, Digital City becomes the flag of city informatization. After the first international symposium on Digital Earth held in November 1999 and the 21st century forum on Digital City held in May 2000 in Beijing, the Digital City construction has become one of the hot important topics. The most active departments, the urban planning and land administration agencies, have set the Digital City construction as one of targets, develop urban fundamental GIS, and make applications one after another. But, What is connotation of Digital City? What are the contents included in Digital City? How to build an urban spatial data infrastructure (USDI)? How to organize, manage and share urban fundamental spatial data? How to use the USDI data in different organizations? Although there has been a lot of research in this field, the well-formed framework and general theory foundation are not yet sufficiently completed to provide instructions to the USDI construction. The study and construction of USDI are just in the beginning stage. Based on the construction of USDI for Digital Wuhan as well as the corresponding application, this paper tries to systematically investigate the questions posed above. The major contents and innovation points of this paper may be summarized as follows:1. The major contents of the studyConsidering the problems in the USDI construction, this paper focuses on the following topics:(1) Outlines the origin, concepts, connotation, contents and framework of Digital City. Digital City is composed of three levels: the fundamental level, the management level and the application level. The core idea of Digital City is to maximize the utilization of information resources. Its kernel technology consists of 3S, the virtual visualization of real world and broadband network. Its basic elements include data, software, hardware, model and service. Its essence is a network-based computer information system.(2) USDI is the foundation of Digital City. This paper analyzes the definition, objective and architecture, the theoretical framework, data classification, key technology, standards, operational mechanism and the data sharing model of USDI.(3) Takes deep study on the data origin, data characteristics, scale, accuracy of USDI, and the coordination of spatial data under different scale and accuracy.(4) Analyzes the integration of urban multi-source, multi-scale data. The contents include thecollection and processing of the multi-source data, the integration and organization of spatial databased on file systems and RDBMS. The advantages and disadvantages of the commonly used dataorganization methods are also compared.(5) Research work about the database construction of remote sensing imagery data. It covers thedata model, data storage, spatial index, data maintenance and management. The compressing,block dividing and database configuring remote sensing imageries are further described.<6) Studies the USDI data management, maintenance and updating mechanism, especially on thedata maintenance and updating methods related to the urban management, and also studies thedata updating technology in RDBMS and the routinely data management.(7) Takes Wuhan as a case study, the Digital Wuhan spatial database is developed which includesseries scaled topographical maps, DEM, remote sensing imageries, geographical name database,3D models for some urban* areas. The data classification and coding, database design, dataprocessing and database construction are discussed.(8)-Based on the USDI of Digital Wuhan, the urban planning and land administration GISplatform is developed. The platform integrates the urban planning data, the land resources data,the urban planning and land resource related project approving documents. The huge data sets aremanaged systematically. The distributed data updating and maintenance mechanism is built up.This system can provides accurate spatial data and decision support for urban planning and landadministration.(9) A dynamic land-use administration system is realized based on the USDI of Digital Wuhan. The construction of the land use database, the usage of DEM in the survey of agriculture land slope, and the land use map updating using high resolution imageries are the key points for research.(10) With the USDI of Digital Wuhan as the foundation, the information of urban planning, approved documents of urban planning and land resources can be published on the internet website. The Wuhan public information service system of urban planning and land resources is built up. It can strengthen the public participation of urban planning, government information opening, and social supervise and service.2. Key technology and innovationsThrough the research work and the corresponding practice, the following achievements and innovative results are reached.(1) By the study of concepts, connotation and contents of Digital City and USDI, the theory framework of the Urban Spatial Data Infrastructure, is put forward.(2) Taking the current data classification standards of the USDI could not meet the demands of data production, updating and easy to use simultaneously, this paper puts forward a new classification method for USDI data for the convenience of data production, updating and maintenance.(3) The four measures: scale, range, detail degree and resolution are discussed. The accuracy requirements of USDI data are summarized. A classification scheme of horizontal positionaccuracy for USDI is produced. As a result, a system of USDI data with different levels of accuracy and scale has been put forward.(4) Considering the current sharing service of USDI is not satisfied, this paper provides a new sharing service mode of base information lease and product value-added service according to the requirement of USDI construction and application.(5) Taking into account the current situation that most surveying and mapping departments in our country have been using CAD to produce topographical maps, this paper extends the semantic mapping methods proposed by the OpenGIS Consortium by introducing the spatial operation into data conversion, and spatial data with different structure can be re-organized or re-structured and quick data conversion can be realized.(6) A new methodology for USDI data management and updating is composed. The change of urban spatial data is mainly caused by human construction, while the construction project must be approved firstly by the urban planning and land administration departments. With this fact in mind, a new idea for updating urban spatial database with the help of documents provided to urban planning and land administration departments by the construction company.(7) As the map sheet is still the production and updating unit of an urban basic topographical map at present, this study proposes the version-revising model for the quick updating of base map by the version updating and the revising updating model.(8) With this study, the preliminary fundamental framework and the spatial database of USDI of Digital Wuhan have been completed. Applications in urban planning, land administration and public services based on above USDI are developed.
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