To be able to write sections like this:

            <layer name="standardplaces" backend="geodata">
                <geodata name="cityplacemarks">
                    <sourcefile format="KML">cityplacemarks.kml</sourcefile>
                    <pick>placemark</pick> <!-- picks certain features from a
                                            file -->
                </geodata>
            </layer>

all related TagWriter classes need to get implemented (just like it has been done for the TextureLayer case before). And unit tests need to get written.

This needs to be done in preparation for the Legend task.