Red-eyed dust bunny
I see why you so many problems with that section. Let's skip ahead for a second, and look at that definition you noted was missing:The next section (p135) is on titles.
A dominion is not a unit of area, it's a political unit. A barony can be one hex (the default size for a 9th level fighter turned new baron), or hundreds. Dominions can also be nested, and it's that nesting that defines the greater dominions like a duchy (not size, by itself).Rules Cyclopedia said:A piece of land that is owned and ruled is called a dominion. It may be of any size, and the ruler can be either a PC or an NPC. A dominion could be a small tower on an acre of land, or a mighty empire with thousands of people. All PC ruler strongholds, both human and demihuman, are called dominions.
Most dominions are part of larger territories; the ruler of the dominion typically swears an oath of service and fealty to a greater ruler. The smallest dominion is called a barony. Any larger area, containing two or more baronies, is very generally called a "greater dominion," and may have any of several names (county, duchy, kingdom, etc.).