In the previous recipe, you were introduced to the basic concepts of the OGC WMS and WFS standards using MapServer. In this recipe, you have done the same using another popular open source web-mapping engine, GeoServer.

Unlike MapServer, which is written in C and can be used from web servers such as Apache HTTP (HTTPD) or Microsoft Internet Information Server (IIS) as a CGI program, GeoServer is written in Java and needs a servlet container such as Apache Tomcat or Eclipse Jetty to work.

GeoServer not only offers the user a highly scalable and standard web-mapping engine implementation, but does so with a nice user interface, the Web Administration interface. Therefore, it is generally easier for a beginner to create WMS and WFS services compared to MapServer, where it is necessary to master the mapfile syntax.

The GeoServer workflow to create WMS and WFS services for a PostGIS layer is to first create a PostGIS store, where you need to associate the main PostGIS connection parameters (server name, schema, user, and so on). After the store is correctly created, you can publish the layers that are available for that PostGIS store. You have seen in this recipe how easy the whole process is using the GeoServer Web Administration interface.

To define the layer style to render features, GeoServer uses the SLD schema, an OGC standard based on XML. We have written two distinct rules in this recipe to render the counties that have an area greater than 5,000 square miles an area greater than 5,000 square miles in a different way from the others. For the purpose of rendering the counties in a different way, we have used two <ogc:Rule> SLD elements in which you have defined an <ogc:Filter> element. For each of these elements, you have defined the criteria to filter the layer features, using the <ogc:PropertyIsGreaterThanOrEqualTo> and <ogc:PropertyIsLessThan> elements. A very handy way to generate an SLD for a layer is using desktop GIS tools that are able to export an SLD file for a layer (QGIS can do this). After exporting the file, you can upload it to GeoServer by copying the SLD file content to the Add a new style page.

Having created the WMS and WFS services for the counties layer, you have been testing them by generating the requests using the handy Layer Preview GeoServer interface (based on OpenLayers) and then typing the requests directly in a browser. You can modify each service request's parameters from the Layer Preview interface or just by changing them in the URL query string.

Finally, you tested the services using QGIS and have seen how it is possible to export some of the layer's features using the WFS service.