So one of the perennial questions that plagues my campaign planning is as follows: “How much space does a tribe of goblins need to be self sufficient? Can I place them in this forest and that’s good enough? Is there also room for these gnolls?”
Now yes, as GM I can do whatever I like, and NO no player has EVER called me on having unrealistic population densities. This is more of a personal guideline thing: knowing what’s realistic or historical helps me make decisions. So, I recently sat down and did some research. Here’s what I came up with:
Acres: An acre (ac) is a unit of area 22 yards by 220 yards. It was historically defined as the area that can be plowed in one day with a yoke of oxen. There are 640 acres in a square mile. Few countries still use the acre, but they’re big ones that include most of our readership, so we’ll include it here.
Hectare: For most of the world, area is measured using the metric system. Though not an “official’ measurement the hectare (ha), a square hectometer, 100m by 100m is commonly used for metric land measurement.
Unit Months: The measurements below are given in acre months and hectare months which as far as I know aren’t a standard unit, but which I define as the given amount of land used for a month.
Modern Agriculture: In our current system, depending on machinery, irrigation and chemical assistance, abundant land produces enough food to feed a person for a year given 8 ac months or 3 ha months.
Medieval Agriculture: Historically agriculture was much less productive. Farming using animal assistance and no chemical intervention on abundant land produces enough food to feed a person for a year given 40 ac months or 16 ha months.
Hunter-Gatherer: The amount of abundant land required to support a single person with a hunter-gatherer agriculture is approximately 3000 ac months or 1200 ha months. However, unlike farming systems which are mostly efficient, hunter gatherer systems are naturally inefficient systems which means they don’t follow a linear production pattern. Thus, when determining the area needed to support X people you don’t multiply by X, but instead by X.75. This is because the more people hunting/gathering the more efficiently they do it. Thus, for example, 1000 people count only as 1000.75 = 180 people due to these increases in efficiency. In theory, these increases would eventually lead to a system just as efficient as agriculture, but that happens well outside the scale we’re concerned with.
Growing season: Because the rates above are in ac months or ha months, dividing the rate by the number of months in the growing season will convert them to ac years and ha years. Because the measurements are the amount of land needed per person per year, this conversion gives you a simple amount of land required per person.
Mass: The rates above are for supporting human sized beings. Food requirements roughly scale by mass, so creatures with half the mass of humans need half the land, while those twice the size need twice the land and so forth.
Unequal production distribution: Especially in large farming societies not all land is worked equally nor is it all of the same quality. While you’re certainly able to break the land into chunks and work out the population each will support and make sure the total population and the total support match, another valid approach would be to multiply the rate by the proportion of land used.
Land quality: Not every culture in your game world lives in the American breadbasket or medieval France where these optimum rates come from. If your setting is less productive feel free to adjust the rates downwards by dividing byÂ a proportion (for example, .5 for half optimum or .8 for 80%).Â Similarly, if your setting is more productive, through the use of magic, more advanced technology, etc… adjust them upwards by dividing by 1 + a proportion (for example 1.15 for 15% above optimal).
Other Forms of income: Plenty of cultures supplement their food production via other methods, primarily trade or raiding. In these cases you can assume a culture supplements their production with some of their neighbor’s excess production and adjust the numbers by multiplying by the proportion of resources that are produced internally. Of course nearby cultures with no excess production are of no use or will quickly starve. These sorts of cultures are classic adventure hooks for your game. Protect the caravan! Stop the raids!
For determining the amount of land required by a group of size X you would use this formula:
|(average rate/growing season) * (1/land quality) * population * relative mass * domestic production||= land required|
|(average rate/growing season) * (1/land quality) * population.75 * relative mass * domestic production||= land required|
Conversely, for determining the amount of people who can comfortably be supported by a parcel of land you would use these formulae:
|land available / [(average rate/growing season) * (1/land quality) * Â relative mass * domestic production]||= supportable population|
|(land available / [(average rate/growing season) * (1/land quality) * Â relative mass * domestic production])4/3||= supportable population|
Correct me if I’m wrong:
Taking for example Medieval rate of 40 acres/month and assuming optimal land, a single guy, and no extra production/raiding for simplicity and lets say an 8 month growing season (40/8) x 1 “normal production” x 1 “single dude” x 1 “human” = 5 acres for 1 guy to eat.
Now adjust the productivity of the land to 75%… (40/8)*.75*1*1 = 3.75 acres for somebody to eat. It shouldn’t take less acres w/ shittier land.
Would it make more sense to make the number 1.25 75% b/c you need 25% more land to make up for your land being 25% less productive? So (40/8)*1.25*1*1 = 6.25 acres for one guy to eat off of…
Or is there a giant hole in my math and/or logic?
You’re absolutely right. I should have divided by those numbers not multiplied by them. I corrected it. Thank you for the heads up. Glad someone caught it. 🙂
I’ve always been concerned with making my settings plausibly realistic, too, but I think you’re going off the deep end. How many players get tripped up on the number of hectare-months of land a goblin hunter-gatherer requires to survive? How many players even stop to ask such things?
As GMs it behooves us to spend our preparation time wisely. My standard is to spend time only on things that improve the game experience. Players are never going to lose their suspension of disbelief over the ratio between acres and Goblins, so I won’t sweat it. I just pick something that seems reasonable and move forward.
Where I do spend time fretting about whether an element of the setting is realistic is when it ties in to the story. How much space does a tribe of 50 goblins need? I might guesstimate anything from a few acres to a few square miles, but more important to me is what’s in that area.
For example, where do the goblins live? Maybe in an abandoned building. If so, who built that building? What was the original use, and when and why was it abandoned? Maybe the goblins overran and killed the previous occupants. These are storytelling elements I can use to bring the PCs into the adventure or connect them from this one to another.
How do the goblins use the space around them? Do they farm? Hunt? Raid caravans? Run guard patrols? PCs will encounter them doing these activities. These will be among the first encounters in the adventure, and the PCs will gradually learn about the setting through them. If they play it well they will learn enough to achieve their objective (kill the goblins, run them off, recover a stolen treasure, rescue a prisoner) while minimizing risk. All great story elements.
What other creatures are in the area? There will probably be other monsters or “neutral hungry” types. What is their relationship to the goblins– masters, servants, rivals, or allies? Perhaps a lone hill giant wandered in to the area recently and has bullied the goblins to serve him. The PC’s objective may actually reside with that giant (goblins were seen taking the treasure or hostage, but they turned it over to their giant master as tribute) and they’ll have to figure that out as the adventure unfolds. More story elements. Also, maybe the giant is too powerful for the PCs to fight directly but they can win by turning the goblins against him or at least persuading them to desert. Even more story elements.
This is the kind of stuff I’d rather spend time on than hectare-acres.
Well, I don’t pretend that my OCD is a common one, but since I looked it up and figured it out I figured there might be someone else out there looking for it too. 😉
Once that lil’ bug was figured out, I found the equations to be quite useful. Though all your points/examples were perfectly-valid/more-obviously-useful, Blackjack, all the fretting’s already been done for us. (Well perhaps I fretted a mild-bit too, but no big).
What we’ve been gifted here is an excellent tool, ready-to-use. It’s already helped reinforce, in my brain-box, the extent to which even very small settlements push outward into the wilderness. As well as giving me a deeper, more structured insight into the relationship between a couple kingdoms in my low-fantasy setting (and in actual history).
I get that most people don’t strive for this level of verisimilitude. However, when the setting feels more genuine to me, that confidence transfers directly to my GMing, my games improve. Anytime a bit o’ math will help my game, I’ll grab a calculator (if it’s simple math, at least). Plus I like these kind of considerations (but I hate really crunchy, rules heavy systems, go figure). I spend too much time considering setting minutia, I’m sure, but I enjoy it. So what-evs.
Anyhoozle, to cut a long rant short(ish), thanks for the formulae(proper-plural?), Mr. Neagley.
On a quick, extra-perspective note, when I run a pulp-style game. Nothing close to this level of detailed forethought goes into it. Genre matters quite a bit too.
Randite, I appreciate your points. I also find that working out certain technical details gives me more confidence in running my game, even when the technical details themselves are not appreciated (or even noticed!) by the players.
Matthew, I hope you did not take offense at my comments. I understand the OCD-ish nature of your effort because I’ve occasionally been tempted to do the same kind of things. In fact, back in college I sat down and tried to start working out the kind of land use calculations you’ve made here.
What stopped me back then was not the conclusion that few players would ever care but the fact that I quickly realized I couldn’t afford the time it would take to complete the research. This was back in the infancy of the Internet, when none of the kind of data or analysis I’m sure you leveraged was available at my fingertips. (OTOH, if you researched this by heading over to the local university’s agricultural sciences library, sought help from a research librarian, and pored though crufty reference indices to figure out these calculations, then my hat is truly off to you!)
No offense taken. I thought your ideas were excellent. I just did an internet search for the info. It still took a few days to dig up though. I can’t imagine doing it pre-internet era. That would make my head spin.
You need to multiply all your figures by 3/2 because unless your goblins are thick as planks they will have figured out crop rotation (the alternative is starving as the land depletes). One year in three a field must lie fallow (aka left to run to weeds).
I’m not sure if those numbers are taken into account in the rates above or not, but I’m sure I’ve missed a million adjustments that could go in there too, so add whatever misc adjustments you think make it work better. 🙂
Thank you for giving me the chance to create an excel worksheet full of formulas to calculate information I will probably never need.
But you never know when you might need it and at least I have it now!
Also, I’m not sure I understand why the formula to calculate the number of people a parcel of land will feed includes the population in it? Isn’t the population the answer? It works when I leave the population variable out.
Wow. I’m in rare form on this article! I corrected the error that Randite pointed out and managed to create a new one. So I’m feeling like a pretty big bonehead.
So thanks for catching my second error of the article. Hopefully I didn’t just create a third one when I corrected the second. :p
No good deed goes unpunished, eh?
Thanks for doing the legwork on this one, though. It really is a helpful article.