In this step, we will determine how much of the world’s surface is covered by water, either as liquid-water seas and oceans, or as a layer of ice. We will express this hydrographic coverage in terms of a percentage. A world with 0% hydrographic coverage has no significant surface water or ice, while a world with 100% hydrographic coverage has no exposed dry land.

This is largely determined by the prevalence of water, from Step Twenty. However, in some cases the amount of dry land surface will also depend on the world’s geophysical parameters, from Step Twenty-One. Large land masses are unlikely to form unless a world has a strong lithosphere and is geologically active, creating variation in topographical relief faster than it can be worn down by weathering and erosion. Otherwise, the world’s surface is likely to be dominated by shallow oceans or ice sheets.

Procedure

Refer to the following table, and find the row corresponding to the world’s prevalence of water and current lithosphere. To determine the hydrographic coverage at random, roll dice as shown in the third column and apply the result.