Ordnance Survey – Great Britain's national mapping agency
![Ordnance Survey home page [logo]](/images/gui/logo-os.gif){kind=logo}
6.5: Web GIS (3)
Internet GIS software
The Internet mapping sites described on the previous page primarily exist to generate user-defined maps. A large amount of map data is stored on the web server, a request for a map is received from a client terminal, a custom image is then generated by software on the server and this image is delivered back to the client within a web page. The software may differ but the end result is a map to look at or print.
The world of the GIS user is also being revolutionised by the Internet. All of the leading GIS software vendors now have products that adopt the client-server architecture. This means the software and data resides on a web server and multiple-client applications access the GIS processing functions across a network. This model is overtaking the use of multiple desktop software installations, especially in large organisations. It can even work across the WWW, and there are many sites that do more than just generate location maps. You can have GIS tools on the web page accessing the full range of GIS functions on the server: selection by attribute, spatial query, thematic mapping, data editing or 3-D visualisation. A major advantage of this model is that the centralised map data only has to be stored and maintained in a single location, meaning users are always viewing the most up-to-date records.
With Internet GIS there is always a trade-off between the sophistication of user tools and response times. Any system that uses the Internet is constrained by the download speed of the connection. The smaller the amounts of data being used and the simpler the client user interface, the faster the application. Internet GIS products differ in the way this balance is approached. Some systems use a very simplistic user front end and display the results of the server-side process by delivering a simple raster image. This means that the applications tend to be fast and robust and will work within a standard browser. Other systems require a client-side plug-in to be downloaded to give richer functionality to the user. Larger amounts of data can be downloaded from the server to the plug-in, which can make the system work more slowly; the benefit, however, is a more sophisticated set of user tools and greater interaction with the data. The choice needs to be made based on the specific requirements of the application and the expertise of the user community.