I was browsing through some of the xml files..WorldGenerator.xml. and WorldParameters...I suppose you could experiment around a bit there. the most obvious being map size:
<?xml version="1.0" encoding="utf-8"?>
<worldParameters>
<size>
<tiny dimension="24 24"/>
<small dimension="32 32"/>
<medium dimension="40 40"/>
<large dimension="48 48"/>
<huge dimension="56 56"/>
</size>
</worldParameters>
The rest is a bit unclear...but It looks like all those 0.2's and such are likely tied to climate selections and such. One would have to spend some time going through all related XMl's to see how it's all tying together. There's an xml for example named "features" as well as one for each terrain type (grass, hills...)
<?xml version="1.0" encoding="utf-8"?>
<landscapeGenerator>
<shape>
<archipelago landTerritories="0.2" patchSizeMin="0.1" patchSizeMax="0.2"/>
<continents landTerritories="0.3" patchSizeMin="0.2" patchSizeMax="0.4"/>
<pangea landTerritories="0.4" patchSizeMin="0.8" patchSizeMax="1.0"/>
</shape>
<ecoregions>
<land>
<feature name="Arctic"/>
<feature name="Desert"/>
<feature name="Tundra"/>
<feature name="Savanna"/>
<feature name="Grassland"/>
<feature name="Tropical"/>
</land>
<water>
<feature name="Desert"/>
</water>
</ecoregions>
<terrain>
<land>
<feature name="Plains"/>
<feature name="Hills"/>
<feature name="Mountains"/>
</land>
<water>
<feature name="Coast"/>
<feature name="Ocean"/>
</water>
</terrain>
<vegetation>
<land>
<feature name="Forest"/>
</land>
</vegetation>
</landscapeGenerator>