Design Requirements for an AJAX and Web-Service Based Generic Internet GIS Client

The development of spatial data infrastructures (SDIs) is broadening out from the current systems which contain largely only Web Map Service (WMS) interfaces offering visualisations of data to more advanced systems offering access to the actual data via Web Feature Service (WFS) or Web Coverage Service (WCS) interfaces and even the beginnings of web-service based access to continuously-collected sensor data via the Sensor Observation Service (SOS) and geospatial processing functionality over the Web Processing Service (WPS) interface. These geospatial web service interfaces are based on standards by the Open Geospatial Consortium (OGC). A common component of current SDIs is a portal which advertises the available services and provides a simple viewer to allow users to explore the datasets which are available. Whilst more advanced users may wish to bind the services into their own desktop client, many users are likely to be satisfied with the web-based thin-client offered by the portal. The recent growth in AJAX (asynchronous Javascript and XML) mapping applications shows how web-based portals may be made much more dynamic. The great advantage of AJAX is that no browser plug-ins (e.g. Java Applet, Flash, SVG, etc.) are required to provide dynamic interactions on the client side. However, the majority of AJAX mapping applications (e.g. Google Maps, Multimap, Microsoft Virtual Earth, etc.) are proprietary, and based on proprietary web service interfaces, and therefore not suitable for integration in a GDI context. Open AJAX mapping toolkits such as OpenLayers are however rapidly developing, supporting a range of open and proprietary services such as Google Maps, Microsoft Virtual Earth, WMS and even WFS.