On the Density of Cities

[Andrew]

I was thinking about the area a massive city would take that I am working into my campaign world and it got me thinking about the common argument and questions of city size and density for medieval or fantasy cities in general. I'm no expert, but with a little reading and some math, I've begun to think about it.

The first question is what can be considered a dense population? 100 people per square mile? 1,000? 10,000?

Why don't we look at it this way. Take the modern "townhome" developments that have been popular within the last decade. Many of those are built on a lot (your total land: house and yard) 3,000 square feet in size. A square mile has 5280*5280=27,878,400 square feet. Divide that by 3,000 gives you roughly 9,300 homes/buildings per square mile. This may be an overstatement due to roads, fountains, common areas, etc, but often buildings built in the confines of medieval walls didn't have yards. So this may be a fairly accurate number. Now just assume an average of 3 people living per building and that gives you nearly 28,000 people per square mile. This is assuming single-family sized homes and other smaller buildings, not skyscrapers. So in theory you could pack 100,000 people into a 2 mile by 2 mile walled city if you so chose with relative ease.

My guess is that the density would be far less, but even 10,000 people would maintain a relatively high density. In fact, Seattle (I looked because I live not far away) has a density of 7,800 people per square mile over about 83 square miles total. We'd definitely consider it a fairly dense city (but not even near the highest) by today's standards. And that 7,800 people includes roads, yards, public buildings, warehouses, stores, etc. So 7,000-10,000 people per square mile is by far doable in a medieval/fantasy city and you could in theory easily double that.

Now if you want a little space, give each home and building an average of a quarter-acre lot (common from the early 1900's-1990's). and you'd get 4 buildings per acre, or 2,560 buildings per square mile. This still gives you a population of 7,700 people per square mile, barring of course roads and public areas. Again, and surprisingly, this is nearly the density of Seattle. A modest home on a quarter-acre lot for anyone who knows gives you ample room for a garden and plenty of yard to mow.

Enough for now, I gotta head to class. I just wanted to give something for people to chew on over population density.

[Arduin]

During medieval time Chang'an had a population of ~1,000,000 for a density of abut 34,000/square mile. Rome was similar during late Ancient period.

[Treebore]

A good one for any CK/DM to bookmark:

http://www222.pair.com/sjohn/blueroom/demog.htm

[Go0gleplex]

It has been my experience while working for a city PW-Engineering & Planning Dept. here in Oregon that planning practices have started to lean more towards common line developments wherein the wall of the residence coincides with the lot line due to Urban Growth Boundary restrictions and such. This is prevalent in multi-family housing such as condos and townhomes. Generally the clustering of such range from 2-10 units. Your lot space of 3000 sf is generous as well. But often times the minimum size lot will be determined by local zoning ordinances depending where you are in the city under modern standards. These types of practices allow for lots as small as 1000 SF with the overall subdivision or plat remainder being rendered as open and/or common space. Typical family size used is 4-5 depending on area in some municipalities. I've also seen them use number of bedrooms to determine occupancy. Don't forget that many residences are multi-story as well. In Italy houses are 25 feet across but three or four floors high for example. The downside to this is fire hazard which is why the practice of having side yard setbacks of 10-20' developed.

Planning practices also reserve area for open space such as parks and avoid development in floodways along rivers and streams. Often times you'll have diversion dikes in older cities along the rivers and such. Generally 5-15% of total area may be set aside for parks and gardens...or open air farmer markets. If your city has walls, there may be set backs from the wall to allow troops to drill or assemble during war.

Best way to approach this would be to outline your city boundaries then divide it up into your slums, working class, trades, and/or affluent areas. Then determine your smallest average residence within that zone. For occupancy; base it on zone again. Slums may have 1 person per 100 sf (10'x10' area) and probably no greater than 1 person per 250 sf. Slums are cramped and squalid after all. Work class zone may have 1 person per 300-500 sf. Trade zone is a bit trickier in that you may have warehousing and or the business may lack living quarters above, though in a medieval setting this would be unusual. So your may have 1 person per 300-800 sf depending on the business. Affluent areas have more estates and yards, plus parks and gardens for the wealthy public. You might have 1 person per 1000 sf+. Remember multi-story buildings. How much of each zone is made up of these...and then adjust the occupancy density accordingly.

[Andrew]

During medieval time Chang'an had a population of ~1,000,000 for a density of abut 34,000/square mile. Rome was similar during late Ancient period.

This actually jives with the website Treebore posted. Under the miscellany section it states the average within the walled confines of a medieval city the population density was 38,800 per square mile.

Be something to think about for campaign builders... I am not concerned with terribly immense depth on density except one of my cities I am working on is a walled behemoth and I was somewhat curious and wanted to put the thought on the subject and pass it on. My thought was to develop a quick cheat sheet for densities of both populations and buildings to help slap cities, hamlets, and villages together in a jiffy.

This is by far not official (or even complete for my train of thought), I just coughed it up as an approximation of what I meant:

Population/Sq. Mile

20,000-30,000/sq. mile -- Heavy density, buildings packed next to eachother. Typically what's found within the confines of a major, walled city.

10,000-15000/sq. mile -- Moderate density, buildings have small walkways/spacing between. Buildings take about 1/16 - 1/8 of an acre including spacing. Good for major city sections outside of walls. Could be those within also.

5,000-10,000/sq. mile -- Light density, buildings on 1/4 acre lots. This is good for smaller villages, hamlets, and the outskirts of larger cities.

<5,000/sq. mile -- Very light density. A couple of buildings per acre.

You could then use the fact that 640 acres occupy 1 square mile to develop a sense of size and population for your cities/villages.