I've gotten back into playing around with sci-fi gaming ( based kinda on Trav, but deviating a bit ). I figure I need to nail down a bit firmer the world building stuff before I begin to work on a universe. I'll begin by generating orbits/distances around a given star in a manner similar to T:2300. The GG's, belts, etc.
Focussing on the main world, in the habitable zone, I'll be generating the physical UWP as described here in a text file;https://sites.google.com/site/moukotige ... /uwp-1/uwp
Trying to describe a culture with Hofstede's cultural dimensions has made me consider that population density is better than total population. This seemed evident when looking at differences between urban and rural cultures, even within a single country such as the United States. This made me think about habitable land and the different population densities of rural vs. urban. Rural populations tend to produce food and raw materials, whereas urban populations tend to be engaged in manufacturing and services.
Agricultural production on non-habitable land need to have some form of life support*, such as listed in the ship building tables for MegaTraveller.
On Earth, habitable land is about 33-38% of total landmass and consists of arable, pasture, and permanent crop land, so it is related to physiological density of population. I chose to use this single datapoint to figure that habitable land is related to land% * hydro%/2. For earth this makes habitable land to be ~10.5% of total surface area, which falls in the ballpark. This makes water act as a kind of limit of land usable for food/people; a world with no water will have no habitable land and thus need life support for food production. Non-habitable land are deserts, mountains, and land without top-soil.
Given all that, I looked at the 'net to see how many people 1 km^2 can support. Many sites agreed with a Cornell researcher that 1 acre could support a single person with a varied diet ( omnivorous ) and given that 1 km^2 has a bout 250 acres ( actually ~247 but I rounded to a neater number ), I figured a carrying capacity of 250 people per square km of habitable land. Using these numbers for earth's dimensions, I get a carrying capacity for earth of about 13.7 billion ( pop number of ~10.137 ), which falls in line with current estimates for max population of earth.
Currently, the earth uses approximately 50 workers per km^2 habitable land ( over varying tech levels ) to grow food. Tech level primarily affects this number of labor. Solar incidence, I would guess, effects growth and thus production, but shouldn't be a big deviation from '1' for worlds in the habitable zone. Again outside of this, a population would have to use some form of life support* to grow food.
so , for a world that doesn't use life support to grow plants,
total world area ~ diameter_km^2 * pi
total land area ~ world area * ( 1- hydro% )
habitable area ~ land area * ( hydro% / 2)
effect pop dens. ~ total pop / habitable land
12,800km diameter = ~514,718,105
land 30% = ~154,415,431
habitable area = ~54,045,401 ( earth pop ~7.5e9 )
eff. density = ~139
If the eff. density is less than 250, then the world is self sufficient and might even be able to export food.
If the eff. density is greater than 250, it must import food or else make up the difference with tech_life_support.
Earth currently does not have a food production shortage as much as it has distribution problems or that many people cannot afford food, which is a separate problem.
* life support might mean something as simple as irrigation trenches to something as elaborate of grow-houses with climate control, lighting, fertile soil created and a water supply piped in.
Technology often tends to increase the amount 'habitable land' available or reduce the amount of labor needed.