Density and size of settlements? (D&D 3.5)

[Strigon]

I've been working on a world for the last few months (well, a continent, but that doesn't change anything), and I've designed the landmass, as well as a few major cities, but I'm having trouble with more population centres.
The continent is somewhat similar to Australia in size, as well as being an island. The issue is, this is a continent run by dragons; dragons are, for all intents and purposes, nobles. If there's a duke, king, or lord, they're almost certainly a dragon, while notable officials like judges, captains of the guard, generals and so on are often younger dragons. I think you get the picture.
Now, naturally, dragons have certain amenities they prefer, and have cordoned off the land to terraform it to each specific dragon type's preferences. There's a northern wasteland, a desert, mountains, forests, swampland, and an archipelago; in short, my continent is a massively expanded version of this: xkcd: Geography (https://xkcd.com/1472/).

In such a world, how frequent would villages, towns, and hamlets be?
What size would they likely be?
Note: Pretty much all of it is inhabited, to some degree. Even the inhospitable places should have significant settlements, sometimes because the dragon is known to be a kind liege, (brass dragons), or because they can't really leave (white dragons).

In case it's relevant, yes their different alignments do tend to make disagreements frequent, but even the most vile of dragons realize that they have life pretty good, and nothing good will come from them rocking the boat too much. They remain fair enough to keep the more kindhearted dragons off their backs, but they'll certainly take any opportunity to gain personal wealth.

[VoxRationis]

Here's the main question. How much do dragons eat? The MM gives a few lines of nonsense about them eating inorganic material, so in your setting, you could potentially make them eat very little, or at least little of consequence. But the typical dragon of legend, the archetype, eats a lot of meat, which demands a wide area and a lot of dedicated bioproductivity to support. If we look at the basic idea of D&D dragons, we see endothermic flyers with enormous body masses, intelligence, and several abilities that should by all rights drain a significant amount of energy; an ancient dragon should eat a LOT. But some people, particularly on this forum, are of the mind that fantasy entails not just suspending disbelief, but flat-out crucifying it, so it might work the other way.
In short, hungrier dragons mean fewer people and more land devoted to livestock, either through agriculture or pastoralism.

[Strigon]

See, that's fine and all until you remember that - in D&D - dragons are also spectacular spellcasters by nature, and there are oh-so-many ways for a dragon to feed itself just by magic. And why wouldn't they? Less food requirements means less space for agriculture, which means more space for industry. And industry gets them all those shiny things they love oh-so-much!

Although that could hold true for younger dragons, who probably eat more to grow and can't yet cast spells; I'll certainly factor that in!

[Aergoth]

Based on your description, if the entire island is cordoned off like this it's quicker to figure out where people aren't going to live. Your desert and frozen tundra are not the sort of places people generally want to live. Humans/humanoids can and will try to live anywhere, they're adaptable like that, but given the ability to move freely and settle, they're going to go for easy terrain. Your archipelago is probably rich in food sources, and the forests and swamps can be worked with in order to render them more habitable to humans and conducive to agriculture. There may be fertile valleys in those mountains as well, and they're a little more defensible against wildlife or hostile humanoids. Basically so long your dragons are prepared to allow the non-dragon sentients to adjust their domains a little there's not a lot of places you can't live.

In the desert you could have regions like the Nile Delta which renders an otherwise infertile region habitable. Or you could have habitation in the north centered around geothermal activity, sort of like what you see in iceland.

If it's anything like australia, your major settlements are going to grow based on resources and accesibility and in the case of an island like this, that probably means coastal. So the further from the coast or a major population center a given settlement is, the smaller it's likely to be and the fewer settlements you're going to find, especially if that's moving towards hostile terrain.

So in the theoretical nile delta, your major population center will be at the end of the river where it joins the next large body of water. Further settlements will be up river from there, and the further from the river and the arable soil it provides you get, the smaller the settlements will be.

Exceptions to this rule can of course be provided by the fact that dragons are dragons. The presence of a dragon might influence the creation of a settlement. This depends on the disposition of your dragons. If they're willing to support and assist the humanoid subjects, the proximity to a dragon of significant power might create a sort of capital, a seat of power that the dragon rules from and that is an attractive place to live. Settlements spring up around this one to provide for the needs of such a place, again growing spaser and more rural the further from that center you get.

[Strigon]

That makes quite a bit of intuitive sense; thank you!

[Everyl]

Another factor that could influence settlement density is the tech/magic level of the setting. The population is going to be higher if agriculture and transportation are more advanced, just because more food is going to be available and it will be easier to move it to where it is needed. Magic might also influence this - preventing/reversing spoilage, creating food where it cannot be readily produced by other means, or use of magic to build infrastructure or aid agriculture. A generous elder dragon has, between its muscle and the magics available to it, quite a bit of potential to enable or accelerate the creation of dams, levees, aqueducts, and other large-scale projects that increase the carrying capacity of the terrain.