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Abstract
The rigorous developments of GIS over the past decades have enabled application developers to create powerful systems that are used to facilitate the management of spatial data. Unfortunately, each one of these systems is specific to a local service, with little or no interconnection with services in other locales. This makes it virtually impossible to perform dynamic and interactive GIS operations across multiple locales which have similar or dissimilar system configurations. The Spatial Data Transfer Standard (SDTS) resolved the problems partially by offering excellent conceptual and logical abstraction model for data exchange. Recent advancements of the Internet enlightened the GIS community as to the realization of an ideal concept of information interchange. A suite of new technologies that embraces Extensible Markup Language (XML), Scalable Vector Graphics (SVG), Portable Network Graphics (PNG) and Java creates a powerful and new perspective that can be applied to all phases of online GIS system development. The online GIS is a Web-based approach to integrating diverse spatial data sources for GIS applications.
To address the spatial data integration options and implications related to the Web-based approach the investigation was undertaken in 5 phases: (1) Determine the mapping requirements of graphic and non-graphic spatial data for online GIS application; (2) Analyze the requirements of spatial data integration for online environments; (3) Investigate a suitable method for integrating different formats of spatial data; (4) Study the feasibility and applicability of setting up the online GIS; and (5) Develop a prototype for online sharing of teaching resources.
Resulting from the critical review on current Internet technology, a conceptual framework for spatial data integration was proposed. This framework was based on the emerging Internet technology on XML, SVG, PNG, and Java. It was comprised of four loosely coupled modules, namely, Application Interface, Presentation, Integrator, and Data module. This loosely coupled framework provides an environment that will be independent of the underlying GIS data structure and makes it easy to change or update the system as a new task or knowledge is acquired.
A feasibility study was conducted to test the applicability for the proposed conceptual framework. A detailed user requirements and system specification was thus devised from the feasibility study. These user requirements and system specification provided some guidelines for online GIS application development. They were expressed specifically in terms of six aspects: (1) User; (2) Teaching resources management; (3) Data; (4) Cartography; (5) Functions; and (6) Software development configuration.
A prototype system based on some of the devised system specifications was developed. In the prototype software design, the architecture of a Three-Tier Client-Server computing model was adopted. Due to the inadequacy of native support for SVG and PNG in all currently available Web browsers, the prototype was thus implemented in HTML, Java and vendor specific vector format. The prototype demonstrated how teaching resources from a variety of sources and format (including map data and non-map resources) were integrated and shared. The implementation of the prototype revealed that the Web is still an ideal medium for providing wider accessibility of geographical information to a larger number of users through a corporate intranet or the Internet cost-effectively.
The investigation concluded that current WWW technology is limited in its capability for spatial data integration and delivering online functionality. However, developing of XML-based GIS data model and graphic standards SVG and PNG for structuring and transferring spatial data on the Internet appear to be providing solutions to the current limitations. It is believed that the ideal world where everyone retrieving spatial information contextually through a Web browser disregarding the information format and location will eventually become true.