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Calculations with Dominionsby Mike Harvey
I've been doing some calculations on the Dominion rules from the RC, so I thought I'd share what I came up with.
I did this work because I'm working on detailing Traladara circa AC960, and wanted to come up with a model for a typical Traladaran dominion. I wanted to know how large a typical farm is. Also, I wanted to determine how many landed knights a barony might support in an 8-mile hex.
An 8-mile hex contains 55.424 square miles (35471 acres). The maximum population for an 8-mile hex is 5000 "families". Assuming the entire hex is fertile farmland and under cultivation, each "family" has a farm of 7 acres. That leaves 471 unproductive acres (1.3%) devoted to roads, villages, waterways, etc.
Medieval grain yields were about 4:1. With 2 bushels of seed, an acre yields 8 bushels at harvest; saving out two bushels for next years sees, that leaves 6 bu/acre harvest. An active person needs about 24 bushels per year for food; inactive persons need about 12 bushels, and the wealthy may consume 48+. One man can harvest seven acres in 21 days, or a bit less than 4 weeks, though he'd prefer to have some help and get done sooner, in case the rains start early.
Let's assume an actual farm family is actually consisting of 2 workers and one child; consumption is 2x24+1x12=60 bushels of food. We'll assign them 14 acres (two virtual "families"); production is 84 bu, consumption is 60 bu, leaving a surplus of 24 bu. There is a maximum of 2500 such farmsteads per hex, so one hex supports 7500 farmers and 2500 other people, or an urbanisation ration of 25% max, which closely matches the figures for Thyatis. It would then take 20 hexes to support Specularum if all land was in production; however it is about 50% forest, so 40 hexes (about 1/3 of the farmland in the duchy) is probably more accurate. However this means that it will take 1200 hexes to feed the population of Thyatis, or 150 24-mile hexes under 100% cultivation -- that is more than the land area of the mainland, even including the mountains and islands. Fish can account for some but it still seems excessive.
So let's increase crop yields to 7:1, allowing for magic and slightly higher than medieval science. Also, let's institute crop rotation, with only 5 acres in production per farm. Those 5 acres can now produce 60 bushels of grain, plus more 4 bushels of food from animals grazing on the two fallow acres. One man can handle this; give him one dependent also. The "family" eats 36 bu, leaving a surplus of 28. Now our hex has a farm population of 10000 persons, and supports an urban population of 5833. This cuts the amount of required land in half.
A population of 10000 commoners is divided into 66 farming villages of 150 (75 "families") each. Each village occupies 470 acres, produces 75 gp in taxes, 750gp in goods and services, plus any resource income. Group the villages in 4.4 sq mi "manors" of 6 villages each, and each manor will support a landed knight with 59400 annual income. A petty baron with one 8-mile hex might have 10 landed knights, plus his own personal manor, plus any hired mercenaries he might want; he'd have an annual income of 59400 plus 118800 in "salt tax" from his knights, for a total of 178200. Of course farming his land out to knights in this manner, he'd only obtain 450 XP per year from his personal manor.