GIS on the Internet

GIS software technology has undergone several revolutionary changes over the past 20 years. The relatively recent expansion of internet technology is now promising to facilitate another quantum leap for GIS and other software applications. The current paradigm shift involves the migration of application software from individual desktop computers into an internet-based client/server architecture. As a result, we are now seeing large-scale development of GIS applications that can be accessed by the user through a web browser interface.

Previously, it was a simple matter to attach static map images to HTML pages and display them through the browser interface. But now, it is possible to connect the browser to a map server application that provides dynamic GIS capabilities including the following:

• Pan and zoom
• Identify functions (point at an object and retrieve its database records)
• Database query
• Control of thematic layers
• Markup and posting of comments back to the server

Map server technology includes a map server application that is run either on a server or on a computer that is directly networked to the web server. The web server software (such as MS Internet Information Server - IIS) is aware of the map server application and funnels any browser-based URL commands (from the internet) to the map server application for action. The map server then processes the URL request, generates a new map image (jpg or gif format) or database listing (html) and sends the location of those objects back to the user's browser.

Figure 1 shows an example of a browser-based zoom and query on the National Geographic's map server website (MapMachine@ nationalgeographic.com).

Major advantages of map server technology include:

• GIS client software is not required, GIS software is installed only on the server. Therefore, GIS access is free of charge (unless a charge is imposed on the server connection). However, some map servers may require installation of a plug-in to run the software.
• The client interface is the web browser. All the user needs for access is a web browser such as Netscape or Internet Explorer with a connection to the Internet.
• The end user does not need special GIS training or skills.

FIGURE 1

Example of a browser-based zoom and query on the National Geographic map server website (MapMachine@ nationalgeographic.com)