Lands around a metropolis

[Altamont Ravenard]

Hello there,

Quick question for some medieval demography buffs out there:

Let's say you have a big city, of X thousand inhabitants. In order to feed that many people, how much land around the city would you need?

I'm trying to come up with a simple formula, ie "1 km radius of land is needed to feed 5000 city dwellers".

I'm asking because I'm putting together a world where there aren't many people left, and where those people congregate in big cities, because the world has become a very dangerous place. I'm trying to figure out how far around the city walls would the city need to control in order to be able to feed every one within the walls.

Thanks in advance for any input, and have a nice day!

AR

 

[gizmo33]

You might be interested in the "Magical Medieval Society" series - you can get them on pdf, they're by Expeditious Retreat Press. There's a lot of info on demographics like this.

Medieval agriculture is labor intensive and so a high proportion of the population would have to live outside the city. One farmer can't farm a million acres to feed a city, right? In fact, without gasoline powered machines, there's only so much land you can plow in a day. And you can only walk so far to that land. And the farmer has to feed himself, and his family and oxen etc.

I believe 3E says that 92% of the population is rural.

Regardless (let's say people have iron golems doing their farming for them) I think you need 1 acre under cultivation for every two persons. Pasture for livestock, woodland for foraging, etc. can increase this value. I use a 1/3 swamp/waste, 1/3 forest, 1/3 farm formula for my game. That means:
population / 2 * 3 = total acres (640 acres = mile, hopefully you can convert to metric)

 

[Altamont Ravenard]

Thanks for the reply.

I SHOULD indeed get my hands on the Magical Medieval Society book, from what I've heard, it's just that good...

AR

 

[orsal]

From the "Medieval Demographics Made Easy" website:

At the medieval level of technology, a square mile of settled land (including requisite roads, villages and towns, as well as crops and pastureland) will support 180 people. This takes into account normal blights, rats, drought, and theft, all of which are common in most worlds. If magic is common, the GM may decide a square mile of land can support many more people.

Obviously, a D&D world isn't "medieval level of technology". It has a form of high technology, namely arcane magic, which likely could increase productivity both of land and of labour. (High-tech agriculture is generally more capital-intensive and less labour-intensive than low-tech, and that should apply to arcane technology as well as real-world modern scientific technology.) So modify the numbers as you see fit, but this could be your starting point.

And I really recommend you read over the web page I just linked if you're trying to work out demographics in any detail.

 

[S'mon]

I use "4 farmers to feed 1 non-farmer" IMC - note that historically city populations _did_ farm - and still often do in some places, eg Russia. 8% urban is about right for the middle ages but you could see a higher urban population in some cultures, eg classical Greece. It varies depending on soil fertility, the principal crop, et al, but historically rarely went below 4-1 AFAIK, and 8-1 or 9-1 would be more common.

 

[S'mon]

For population densities, I use 50/square mile as typical, up to about 120/mile for fertile realms (like medieval France) - Britain's population in the middle ages averaged only about 20-40/sq mile though, and a campaign set somewhere bleak like the Scottish Highlands might have it as low as 10/square mile. Avoid the common mistake of giving the High Kingdom of Furyondy a population of 1/square mile though, at those densities anything other than scattered hunter-gatherers is effectively impossible.

 

[S'mon]

For population density in big cities like Rome or London I use 50,000/square mile; a small town would be more like 25,000/sq mile and occupy much less than a square mile of course.

 

[Tonguez]

For sake of ease I just assume that the Metropolis population includes the rural adjuncts (towns and villages) that support the Urban center. This way I can gloss the actual area and just say something like "the lands around Gotham are planted in cabbages and corn with villages scattered throughout. Each market day the roads are clogged with farmers carrying their produce to the city market..."

 

[Hand of Evil]

I just roll a d20 for number of towns within 30 miles of a metroplis, a d12 for 60 miles, a d8 for 90 miles but I like wildernesses.

 

[philreed]

I'm trying to come up with a simple formula, ie "1 km radius of land is needed to feed 5000 city dwellers".

This sounds exactly like one of the diagrams I put together for the new edition of GURPS Fantasy.