Are you ready for building maps? We can do this without GeoServer; indeed we will install it in the next chapter. For now, you will play with an online map engine and Google Earth to try your understanding of thematic maps concepts.
Point your browser to http://thematicmapping.org/engine/.
Choose a statistical Indicator from the drop-down list, that is, CO2 emissions, then select Year as 2004. Leave all other values as the proposed defaults.
Select the Preview button; a pop up will show you a Google earth plugin with countries rendered in different colors according to CO2 emissions in world countries.
Now try a proportional symbol map. Select Mobile phone subscribers per 100 inhabitants as Indicator and 2006 as Year. Choose Proportional symbol for Technique and Regular polygon as symbol style. Select circle from the drop-down list. Leave the default colors unchanged and select Equal intervals for classification.
You built a couple of thematic maps selecting data, symbol size, and color. You will need to set exactly these parameters in GeoServer to produce beautiful maps. This time we did it without exploring the technical details behind features rendering. In Chapter 6, Styling Your Layers, you will learn how to use SLD (styled layer descriptor) to make thematic maps.