Web Mapping Illustrated

Walkthrough of the Main Components

MapServer produces output graphic files based on the input requests from the user and how the map is defined. Key components include the MapServer executable or CGI program, a map file, data sources and output images. Figure 4-3 shows how all these components work together: after a user request, the MapServer CGI program accesses a map file, draws information from the data sources, and returns an image of the map.

Figure 4-2. A map showing various layers of information

MapServer Executable

The simplest form of MapServer runs as an executable CGI application on a web server. Technically, MapServer is considered an HTTP-based stateless process. Stateless means that it processes a request and then stops running. A CGI application receives requests from a web server, processes them, and then returns a response or data to the web server. CGI is by far the most popular due to its simplicity: no programming is required to get it working. You edit the text-based, runtime configuration file, create a web page, and then set them up to be served by a web server.

Tip

If you are a programmer, you don't need to use MapServer in CGI mode. Instead, you can create custom applications that use the MapServer API. However, this is considered an advanced topic, and an overview is discussed in Chapter 14.

Figure 4-3. Main MapServer application components

The MapServer CGI executable ...