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An exploration of GIS architectures for Internet environments

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Abstract

The World Wide Web and the Internet have great potential in improving accessibility to spatial data and to spatial data processing services. We explore this theme by reference to three recent developments, demonstrating different architectural approaches to spatial data distribution. First, the ACT Pilot system assesses the feasibility of transferring cadastral data over the Web in vector form, to facilitate interaction based around the map image. Secondly, the Hydra-4 project extends the vector-based map interaction for environmental mapping in an interactive system for water quality planning. Hydra-4 enables Web access to both spatial and temporal data. Thirdly, the on-going SMART project assesses the technical feasibility of spatial Internet marketplaces, in which applications are built from data and processing services offered by multiple, independent providers. A small SMART demonstrator system has been built.

Introduction

The World Wide Web (the Web) has become an immensely valuable information resource. It is a compelling example of the synergy that can exist between new technology and the new applications enabled. The appeal of the Web stems from the combination of the near-global reach of the Internet, the ease of publication of information, and the simplicity of access by users to that information. Not surprisingly, there is high interest from spatial information systems (SIS) researchers, practitioners and vendors in exploiting the Web. The primary exploitation to date has been to distribute spatial data products, widely and conveniently. For example, a local government body might use an intranet to distribute cadastral maps to its policy and operational units, without having to equip them with specialist software. Indeed, the compact and informative nature of map-based presentations makes them attractive to a wide variety of Web information providers.

In this paper, we consider two themes in the use of the Internet by the SIS community. The first is the extended use of the Web for distribution of spatial data. Of particular interest is support for the richer set of interactions with spatial data expected in conventional geographic information systems (GIS) but not readily possible with the standard Web tools. The second is access, using the Internet, to specialist spatial data processing services.

The Web's pervasiveness is enabled by its client–server architecture. Data storage, extraction and processing functions are performed at the remote server, while presentation functions are performed at the local client by an off-the-shelf browser package. Simple standards enable a choice of browsers, including Netscape Navigator and Microsoft Internet Explorer. There are already many impressive Web sites offering spatial data products under this architecture. These first-wave combinations of SIS technology and the Web deliver spatial data as hypermedia documents. At the server, a raster image (usually in GIF format) is generated, either by conversion from a vector map or by extraction from a database of raster maps held as georeferenced images. At the browser, the image is viewed using the standard image display tools, generally built into the browser itself. Specialist SIS tools are needed only on the server.

This strategy is effective for the many applications requiring only standardised products but it depends on only very limited client functionality. For example, when the user chooses to pan, zoom or toggle the presentation of map layers, a request to the server for a new image must be made. The approach is clearly ineffectual when there is a need for significant interaction with the spatial data or extensively customised displays. It is attractive to consider more sophisticated approaches that offer a richer set of interactions and lower data communications costs. We explore some approaches to this issue in the next section through analysis of the design and performance of a system for Web distribution of cadastral and related data. The system links property maps with aspatial data such as ownership, sales and valuation information. In the following section, we describe another application of the principles for map-based interaction in a system for Web distribution of spatial, aspatial and temporal data related to water catchment planning.

It is also interesting to consider how the Internet might be used to allow an application to draw on remote processing services. A geographically dispersed organisation might prefer to mount specialised software on a central high-performance computer, enable access from other sites, and thereby avoid the costs of installation and maintenance at every site. Smaller organisations might wish to access an external service provider for specialist software and hardware that is used too infrequently to justify purchase. In Earth observation, for example, many operations require extensive processing and some applications call for rapid generation of products. An analyst needing geometric correction and enhancement tools in order to estimate wheat production might use high performance computing services at a remote site in preference to more limited local facilities. The question, then, is how best to use the Internet to provide access to such services. In the section on spatial Internet marketplaces, we present the concept of a spatial Internet marketplace, essentially an infrastructure for the publication of processing and data services. An architectural model is offered and is demonstrated by a simple application for itinerary planning. In the Conclusions section, we consider the more general implications of the new application of SIS technology enabled by the Web and the Internet.

Section snippets

System architectures

The Web is a client–server environment specifically designed as a distributed hypermedia information system. The standards for interfaces between clients and servers in the Web are relatively light, and permit a large number of approaches. A useful primary categorisation of the approaches can be made in terms of the assignment of functions to the client and the server. The extremes are then the “thin-client, fat-server” and the “fat-client, thin-server”, whereby “thin” implies a minimal amount

Hydra-4

The second project dealt with using a map-like user interface to access a diverse collection of data. Here the emphasis was on map production from vector and raster data and on access, through point-and-click on map features, to temporal data presented as a graph. Because the map was to provide the primary working surface for user interaction, an efficient approach to map display was critical to this project.

The project, a collaborative effort with the Sydney Water Corporation, aimed to publish

Spatial Internet marketplaces

So far we have considered Web-based access to end-user spatial data products, and have accordingly emphasised data presentation and visualisation. But the Web also readily supports the publication and distribution of data products in standard formats that are intended as input to customised data processing. A supermarket chain, for example, might retrieve demographic data for the regions around its outlets. It might use that data together with its private sales data for outlets to compare their

Conclusions

The Web has already had a major impact on SIS through improving the accessibility of spatial data. The broadened market base for SIS practitioners and researchers will, almost certainly, be influential as a driver for research and development. There remain some applications that are handled only with great difficulty with the current off-the-shelf tools. A challenge for researchers and practitioners will be to determine where these applications are better addressed by innovative use of

Acknowledgements

The work presented was pursued by a team of which the authors are members. This paper draws on the contributions of our colleagues in the Spatial Information Systems Project of CSIRO Mathematical and Information Sciences, and we gratefully acknowledge the many contributions of Volker Gaede, Dean Jackson, Rob Power, Dean Kuo, Gerritt Riessen and Xiaofang Zhou. We are also indebted to colleagues from industry and government who have alerted us to challenging research issues and supported our work.

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