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Web Based Data networks
Difficulties in disseminating data have meant that more often than not the same data is duplicated by each organisation using it – a complete copy of the same base map can be at each organisation access it. It is not uncommon for the same dataset to be duplicated even between different offices and departments within the same organisation. This is not only wasteful in storage; it incurs a significant overhead in data management and update, and inevitably leads to inconsistency between the datasets used by different organisations (or parts of organisations).

Web based data networks seek to promote data sharing between organisations and permit multiple organisations to locate and utilise a single copy of a dataset without the need to duplicate it. This initiative differs from data warehouses that sought to concentrate data management of all required data in a single massive database. Where data warehouses fail is in the understanding that often data is best maintained and stored at source – with the organisation that is responsible for collection and update – rather than in massive centralised systems.

The data network is designed around the web services concept of Publish, Discover, and Use. Data service providers are responsible for maintaining their data and for making it accessible to other users on the web. Such access may be permitted free of charge (as in the case of some Government’s or international organisation’s datasets) or on a subscription or one-off-charge basis. The provider is also responsible for providing a basic description of the service that can be posted to a central registry. Documentation includes metadata (such as the Federal Geographic Data Committee (FGDC) or ISO standards), as well as a service description increasingly provided using the Universal Data, Discovery and Integration (UDDI) and WSDL protocols.

At the heart of the network is a central web site that acts as registry or ‘Yellow Pages’ to which data providers can register their service and through which users can discover data offered. If the user decides to use a service, the register will pass them to the respective data provider’s site from which data can be drawn directly. The adoption of open Internet transfer standards (such as GML or ArcXML) means that an increasing number of desktop GIS applications can directly read and integrate such data drawn from the web. Using a package like ArcView or ArcInfo, for example, a user can now integrate and work with data from a local hard-drive, network and multiple web sites. The result is an open, multi-participant, community based network that encourages data sharing and communication.

This has a number of implications:

• Clients do not need to maintain their own copies of standard datasets – they can be accessed directly from the supplier;
• Suppliers can provide more flexible data supply contracts based, for example on: intensity of usage and/or areal coverage, which can be tailored to meet the specific needs of a client;
• The introduction of economies of scale can permit levels of investment in data update and maintenance and the provision of server security and backup facilities, that are well beyond the means of most organisations, providing not only better quality data, but also real 24:7 reliability of service;
• Competition brought about by publishing the availability of data will ensure that data supply costs are kept to a minimum.

The Geography Network launched by ESRI in June 2000 pioneered the concept of spatial data networks. The Geography Network was established as a registry and discovery engine for spatial data and application services offered by a large number of public, private and commercial organisations. Highly scalable, the Geography Network model has been duplicated around the world (e.g. in New Zealand, UK, Holland, Hong Kong), with each new node linking into the wider network framework. The Hong Kong G.Net (www.gis-webservices.com) is illustrative of this trend.

The Hong Kong G.Net (HK-G.Net) offers an expanding range of datasets covering HK SAR including:

• general base map information;
• demographic and census data;
• point of interest (PoI) at various levels (public services, commercial, tourist etc.);
• Yellow Pages location directories;
• a complete navigable road network (including turn directions);
• Orthophotography; and
• Satellite imagery.

These datasets are derived from a range of data suppliers both commercial and public, and are either hosted locally by the HK-G.Net itself, or by the suppliers themselves. The G.Net site permits data to be viewed, searched and interrogated. As data is served in ArcXML, live data can be served to any ArcXML compliant application. Some of the datasets (for example imagery and census data) require payment before they are made available to the user, either on a one-off purchase or subscription basis. The registry handles payment through direct linkage to 3rd party payment gateways.

The HK-G.Net is not only permitting greater access to, and integration of, a wide range of datasets, it provides location search and mapping functions in the form of web service components. The Simple Open Access Protocol (SOAP) wrapped location and visualisation functions permit organisations to integrate maps and spatial search functionality directly into their local applications/site. Thus for examples, banks and property agents that do not, themselves have any GIS or mapping software, are using the service to integrate maps generated by the Hong Kong G.Net into their own websites and internal systems. They do not have the additional overhead of purchase and management of separate software and datasets, and are assured up-to-date, accurate mapping provided in a format that can easily be integrated.

As the Hong Kong G.Net is part of the wider Geography Network framework, it exposes local datasets to the global community – helping to provide awareness of the highly detailed data resources in one area of the world and to make these readily available for potential users. As more organisations establish web based data networks the volume of data that can be easily searched and accessed is increasing dramatically.