Design And Implementation Of Map Sharing System Based On WebGIS

21st century is a new century of human development and utilization of the oceans. As a developing coastal country, China proposed the "Digital Ocean" development strategy at the turn of the last century. It is very important to safeguard national maritime rights and interests effectively, develop and utilize ocean resources rationally, protect ocean ecological environment, realize sustainable utilization of ocean resources and environment, and develop marine affairs coordinately. Ocean spatial information sharing is an important component of "Digital Ocean" strategy.Meanwhile, with the rapid development of distributed computer technology, Object-oriented technology, network technology and the gradually popularize of internet in the global, WebGIS began to appear and has been an important research direction of GIS. WebGIS presents the geographical information and GIS service with more wide application fields. WebGIS can also make GIS enter into people's daily life, and provide a good development ideas of realize GIS's socialization.Based on these considerations, a solution of massive map's sharing and fast access using WebGIS and other advanced technologies were studied in this thesis. This thesis was funded by the National 908 Project. Firstly, the theory of WebGIS, including basic concepts, characteristics, system frame and several mainstream implementation methods, were introduced. And then, the characteristics of these implementation methods were compared. According to the data quantity, application environment, Multi-user's concurrent access and other features, the map implementation strategy and constructive mode of sharing system were designed in this thesis. Also, the prototype system proposed in this thesis realized functions of map data organizing, uploading, publishing and browsing.In order to improve response speed, the key influence factors that affect system performance were detailed in this thesis, and several strategies which can shorten map-accessing time were proposed, including Image Caching Strategy,Double-thread and Double-caching Strategy,Breadth-first Intelligent Prefetch Strategy,Depth-first Intelligent Prefetch Strategy and Farthest-distance Cache Replacement Strategy. In this system, sliding window data transfer is used to accelerate the map transmission speed.Finally, a system performance test of before and after optimization has been made.The testing results showed that the time required for map browsing was reduced significantly and the system response speed was improved effectively by using the proposed strategies.