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Background

I'm creating an island on a medieval world with one large port city/town and roughly half a dozen smaller settlements on it. It's not too far from the mainland—several hours at most—but big enough to have a mostly self-sustaining population of its own.

Conceits of the Setting

  • The island is in a temperate zone, south of the equator
  • It's a fantasy setting, with magic. But it's not that widespread
  • The island has been civilized for hundreds of years
  • Up until recent history (less than a 5 years) it's been kept safe by a powerful empire
  • The empire is a generic continent-spanning, mostly-good (but sometimes harsh) empire
  • It's a generic D&D/Warhammer Fantasy setting

Reasons for Asking

I'm a role-player, and creating this island setting for running my players through a few adventures. I have no idea about population density, appropriately sized land masses, medieval-like city/town/village populations, and everything that follows from them.

Questions

  1. How big of an island would this theoretically be? In square miles/kilometers (I'm American, so sq mi would be easier, but I can do the conversion from sq km)
  2. What would the total population of the island be, and how would it be distributed? I know that a majority will be in the port city/town, but what about the outlying towns/villages?
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  • $\begingroup$ I think the question would be improved by some clarification of what you mean by "large" in your first sentence. Not having more detail there is why I had to make up the "two bookshops" idea in my answer--I'd have preferred to baseline everything off of something in your question, though! $\endgroup$ – nitsua60 Sep 23 '15 at 14:13
  • $\begingroup$ @nitsua60: that is one of the reasons I posed this question. I know nothing about populations and what is considered average or large or any of that. The only thing I knew for sure that I wanted was a half-dozen villages being supported by the port city/town. Knowing that, I was hoping someone could help me figure out what size population would work, and how "large" of a settlement it would be: city, or town. $\endgroup$ – Christopher Sep 23 '15 at 15:24
  • $\begingroup$ Maybe then edit the title to be "What should the population of a one-city island be?" Then your body can get at the auxiliary questions: geographic size, distribution in and out of towns, &c. I don't think it's a big deal, just trying to improve the benchmarks so that future answerers don't have to speculate as much. But I could be overthinking this--you got two very good answers, either of which (I think) answers the question you had. That's a sign that the question as posed was just fine! $\endgroup$ – nitsua60 Sep 23 '15 at 16:10
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Try Medieval Demographics Made Easy (MDME), an excellent article written specifically as a guide to creating the population distributions one might use in Fantasy Role-Playing. Here's an example of how to use it, with your "I want one port city" benchmark, to get the rest of the numbers you might like:

I need a city with competing bookshops, for plot reasons. Two, maybe.... Okay, then this city has a population on the order of 13000 people. Let's say it's the biggest city. This makes the whole island's population somewhere around 75000 people. Let's make it densely-populated, like a Sicily: 90 ppl/mi2 means the island's size is 833 mi2. Densely populated, small island should be pretty fertile (or else why keep having so many babies!) so lets go with each mi2 settled supports 250 ppl: 300 mi2 settled for about 36% settled, 64% wilderness. No other cities, just towns numbering a half-dozen or so. Call it a 20 mi$\times$40 mi rectangle and you're basically done.

(I just used the expectation values for all rolls called for in MDME and rounded liberally. You might want to tweak so as to get at your preferences. For instance, 2d4 rather than 1d8 for number of villages.)


Bonus Example, to illustrate how a different benchmark could play out: my island would take ten days to cross on foot. Okay, now we're a 240-mile diameter island, or ~45000 mi2. MDME gives me some guidance on likely densities; this is a backwater part of the empire, so I'll pick the number from medieval Britain, 40 ppl/mi2, giving me a population of 1.8 million. The Agriculture section tells me that about 10000 mi2 need to be settled in order to feed those people, so the island's about 20% settled, 80% wilderness. The Population Spread section tells me the largest city should have about 20000 people, another one around 10000 people, and there'll be about 18 towns ranging from 1000 to 8000 residents. &c. &c. &c.


Further Reading for your particular example: The Edge of the World: A Cultural History of the North Sea and the Transformation of Europe by Michael Pye, esp. pp.177--191 which give great detail of everyday life in areas dependent on fishing, on fishing vessels, and business practices related to the development of commercial fishing, &c.

Furthermore, there is a practical calculator available online here, sourcing from MDME.

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  • $\begingroup$ That is a fantastic website. I can't gauge its accuracy but it seems pretty solid to me. $\endgroup$ – James Sep 22 '15 at 13:32
  • $\begingroup$ The way to gauge it is to read the sources in his Bibliography. I've read some, and they're fascinating--they also deeply inform my GMing, especially in the small details. Construction materials for a single-family dwelling, how farmhouses cluster in valleys, how 'normal' folk spend their days, &c. &c. &c. A recent read I'd recommend is The Thief-Taker Hangings, richly describing the lives of rogues in 18th-C. London. $\endgroup$ – nitsua60 Sep 22 '15 at 13:44
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This depends largely on your story.

For a large medieval town, you can reference almost anywhere, but there was a successful port town of Castelsardo, in Italy, which I seem to recall was an island, or very nearly. It had a climate such as you describe.

  1. Wikipedia says it was about 17sqmi (45km2).
  2. Our tour guide said at its height, during the medieval ages, was 5,000 people.
  3. EDIT - Therefore a nice, typical medieval city could reasonably achieve 300 people per square mile, and function well on trade routes, fishing, and security (your central castle) economies or activities.

CAVEAT

ALL of this is very generic, because the answer depends HIGHLY on more information needed in your question - size of the kingdom, availability of materials, trade routes, etc. These you may use to adjust these numbers.

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  • $\begingroup$ My problem is that I don't know where to reference, so "anywhere" isn't very helpful. As for the rest, I'm actually doing this for a role-playing game, so it's a "generic continent-spanning empire in a generic D&D setting." I want it to be big enough for several adventures, and enough room for the party to explore, but not so big that they can't map it all if they wanted to. I'll update my question with this information. $\endgroup$ – Christopher Sep 21 '15 at 18:19
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    $\begingroup$ Start by googling, for example, Castelsardo (en.wikipedia.org/wiki/Castelsardo). You can use some of the images if you want visuals for your players, and you could even draw up maps from the real place. Read about its history. But really, I have found all the time spent by GMs to create detailed geography, history, etc is mostly wasted, especially on D&D players who don't care how accurate your maps are...they just want to kill things and collect treasure. Flavor text is nice but the RL accuracy of that flavor text is largely irrelevant. $\endgroup$ – Francine DeGrood Taylor Sep 21 '15 at 18:43
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    $\begingroup$ @Christopher - That is an excellent second question you might ask: "What are the parameters to help support a large medieval, island city;" then give details on what you want to achieve (look, feel, size, etc.) of your city. We will work backwards to 'build' your world. Sorry I know nothing about D&D, but Francine's answer sounds like a good start. $\endgroup$ – Mikey Sep 21 '15 at 19:04
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    $\begingroup$ @FrancineDeGroodTaylor It's not wasted if Christopher enjoys doing it. Worldbuilding--as this site exemplifies--can be a fun game to pursue for its own ends. That said, if all Christopher wants is a usable map so he can get to other things he enjoys more, I'd +\infty your comment-suggestion of grabbing a historical location. "Where should people live on an island on the outskirts of an empire?" is a solved problem. $\endgroup$ – nitsua60 Sep 22 '15 at 4:22
  • $\begingroup$ @nitsua60 It would be user intent in this case. In this case, I believe that the answerer intended to draw attention to the new part to highlight how it helped answer the revised question. But I just changed it based on writer intent. A more common reason to signal is that it responds to a comment. $\endgroup$ – Brythan Sep 23 '15 at 3:21
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I cannot say precisely what population density an island like that could sustain.

I'd suggest a town population of ~10,000 and a rural population of ~3000 (2000 + 1000) for the island. If it is an action game, you could place watch towers at some points. Also, don't keep the terrain all plain. In order to give archers a natural advantage in some places, keep v1 or v2 on higher grounds.

I could give you some ideas on the map of the island. Let the town be fortified with a wall and gates. Also, let i2 be a privately owned island by some villain in the game and i1 be a deserted small patch (where you can let your main character build his little base one point in the game). Have some adventure(s) where the hero has to travel from v1 to v2 but force a boat trip.

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  • $\begingroup$ Where are you getting 75% town and 25% rural from? That's nothing like the pre-industrial numbers--the typical baseline for fantasy RPG--that I've seen. $\endgroup$ – nitsua60 Sep 22 '15 at 4:16
  • $\begingroup$ My bad. But for places centered on one profession (fishing here), central population tend to be denser than the suburbs, even for medieval societies. I was wondering about Mayans and Aztecs and their island cities ... $\endgroup$ – Youstay Igo Sep 22 '15 at 4:23

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