Design And Implementation Of WebGIS Based On JavaScript Technology

The rapid development of the Internet, drives quick update and development of the current GIS technology, and provides GIS with a new and effective geographic information carrier. Nevertheless, the further development of GIS will face the problems of heavy burden of mass data processing and the bottleneck of network transmission.JavaScript can make a variety of tasks be completed only on the client without the participation of networks and servers, and it support distributed computing and processing. So, the application of JavaScript technology in WebGIS, greatly reduces network transmission and burden of the server. In this situation, all the GIS operations are done locally, the server only provides GIS data services, and it also only have a one-time data transmission.The thesis introduces the WebGIS structure, developing models and all kinds of technology to implement WebGIS, scientifically analyzes the traditional defects of electronic map development from the view of architecture, and designs a new WebGIS implementation model based on JavaScript. In the thesis, it builds a whole WebGIS and designs its modules, which includes electronic map view, spatial measurement and spatial layer development. On the way of geographic maps provided, it is not the traditional way, which the server generates grid picture from mass vector map and sends it to the client, but a new way which the server immediately send many prepared slice pictures to the client. On the display of the map, it uses a new way which client pieces a number of slice pictures together to show the view, instead of a whole map shown. On the development of the spatial layer, using Ajax development model and VML(The Vector Markup Language), it designes a storage structure of the spatial layer, and some performance model of spatial layer. And it gives a very good solution about the overlay between the grid picture and vector map.By the evidence of constructing Dalian WebGIS, the model improves the efficiency of the WebGIS, and has good effect in practice.