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 Post subject: pop related junk
PostPosted: Wed May 03, 2017 2:41 am 
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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.

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Last edited by Ishmael on Fri May 05, 2017 6:25 am, edited 1 time in total.

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 Post subject: Re: pop related junk
PostPosted: Wed May 03, 2017 5:28 am 
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This is good stuff. I have a couple of things to add.

First is tech level. At low tech levels where you don't have motorised agriculture a lot of your primary agricultural production has to be fed to traction animals for the ploughing, which reduces the effective carrying capacity. Either you feed grain to horses or you put land aside to grow fodder for oxen. Petroleum fuels are transitional; high tech tractors are probably electric. Then there is the question of enough agronomical science to know what fertilisers to apply and enough cheap transport capacity to deliver them in quantity where they are needed. And the tech to produce, deliver, and apply pesticides.

Subsidiary to that is the issue of how highly-domesticated your crops are. A planet that has domesticates such as maize, potatoes, rice, wheat, bananas/plantains, manioc etc. has a higher carrying capacity than one that lacks them. During the Green Revolution of the Sixties and Seventies plant breeder like Norman Borlaug produced new strains of crops that are two to three times as productive as the Neolithic domesticates (though sometimes dependent on more fertiliser and pesticides). In the future we might replace modern crops with ones that have been heavily modified, or biologically engineered from the ground up, to be even more productive than Borlaug's dwarf wheat and rice. An ideal crop might be a deep-rooted perennial that fixes its own nitrogen, is self-mulching, is immune to natural diseases and intrinsically inedible to pests, and bears its crop (not necessarily a fruit or seed) on an emergent stalk for easy harvesting. A high-tech field might need no annual tillage or planting, and have the economics of a plantation. In an SF setting it is possible to imagine that by trade, aid, or technological collapse you might get societies that are in a general way low-tech, but that have viable legacies of highly-domesticated of biologically-engineered crops developed at a higher tech level.

Second, there is the issue of surface illumination. The primary productivity of plants in agriculture is limited by the availability of water and plant nutrients, but it consists of converting the power of sunlight into chemical energy and is fundamentally limited by the availability of light of suitable wavelengths. A planet with a stronger greenhouse effect than Earth's, or cooler than Earth, or with lower albedo than Earth can have an equable temperature while receiving significantly less insolation than Earth does. Then the total production of agriculture would be reduced in line with the brightness of sunlight at the surface. Or the factors could go the other way, and the planet might be brightly-lit without being excessively hot.

The most significant factor here might be the colour-temperature of the star. I think there are good reasons to believe that, for any life based on organic chemistry, UV and IR light are pretty much unsuitable for driving photosynthesis. The energies of photons just don't match up with the energies of chemical bonds in the right way. The temperature of a planet is determined by the bolometric luminosity of its star (and albedo, greenhouse effects etc.) but its surface illumination is determined by its visual luminosity, which means that for a star of spectral class giving a significant bolometric correction, planets with the same sort of temperature as Earth my be significantly dimmer-lit or slightly bright-lit than Earth, with primary agricultural productivity scaling directly with visible illumination.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts on SFRPG must not be reproduced beyond the board except with explicit permission from me.


Last edited by Agemegos on Thu May 04, 2017 9:38 am, edited 1 time in total.

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 Post subject: Re: pop related junk
PostPosted: Wed May 03, 2017 6:04 am 
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Here's my table of relative visual brightness as a function of spectral type. I calculated the values from bolometric corrections, some of which I interpolated between standard values. It does not take into account luminosity or the inverse-square effect. That is, the visible illumination of a planet's surface equals its insolation times this factor, so the brightness of the sunlight (and the primary productivity of vegetation) is equal to Earth's times the absolutely luminosity of the star, divided by the square of the planet's orbital radius, times this factor.

type relative visible brightness
M7 0.0283
M6 0.0389
M5 0.0537
M4 0.0741
M4 0.102
M3 0.141
M2 0.194
M1 0.268
M0 0.370
K8 0.428
K6 0.497
K5 0.577
K4 0.670
K2 0.777
K0 0.902
G8 0.926
G6 0.950
G4 0.975
G2 1.00
G1 1.03
F9 1.03
F8 1.04
F7 1.05
F6 1.06
F5 1.07
F4 1.07
F3 1.08
F2 1.09
F1 1.10
F0 1.11
A9 1.10
A7 1.09
A6 1.08
A5 1.07
A0 1.02

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— Brett Evill

My SFRPG setting, Flat Black

© My posts on SFRPG must not be reproduced beyond the board except with explicit permission from me.


Last edited by Agemegos on Wed May 03, 2017 9:22 pm, edited 1 time in total.

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 Post subject: Re: pop related junk
PostPosted: Wed May 03, 2017 1:16 pm 
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The comment about insolation reminded me of The Expanse, where Ganymede's agri-domes requires the use of orbital mirrors to focus sunlight. Harder to do around a larger planet, probably?

S John Ross wrote up a thing about medieval populations and % of the pop devoted to agriculture.

Quote:
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.


So that's for, I guess, TL 1 in Traveller terms. But an interesting comparison. To support pop 9 at that TL, you'd need more than 5 million square miles, or 14 million sq km, devoted to agriculture. That's about 7 percent of the Earth's surface, and 25% of Ish's calculated habitable area. That is a LOT of farmland.


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 Post subject: Re: pop related junk
PostPosted: Thu May 04, 2017 9:44 am 
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Agemegos wrote:
At low tech levels where you don't have motorised agriculture a lot of your primary agricultural production has to be fed to traction animals for the ploughing, which reduces the effective carrying capacity.

To be explicit about "a lot", I have read that before the invention of steam trains two-thirds of the crops (including hay, grown in irrigated "meadows") were fed to draught animals. I guess that includes horse-drawn transport as well as the ploughing (which was far more significant), on the other hand it does not include vegetable oils and wood grown for lighting, cooking, and heating fuel.

That is, mechanising tillage and transport may have tripled the carrying capacity of some environments.

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My SFRPG setting, Flat Black

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 Post subject: Re: pop related junk
PostPosted: Fri May 05, 2017 6:56 am 
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I don't think that I want to go into any amount of detail as to exactly what the tech innovations actually are, but I just want to work out how technology levels affect output and number of workers per sq km. I will be using a tech level progression 'inspired' by Traveller to try and keep things somewhat compatible, but where the tech number represents a major shift, perhaps a paradigm shift in technology, and the decimal represents advances within that shift.

I only have a couple of data points to figure out how tech affects production per sq. km, or workers needed per sq. km., but I have to hope to work something out based on data from the site, http://www.nationmaster.com ( in my case, http://www.nationmaster.com/au ). Naturally, it won't give traveller tech info directly, so I'll have to work that out by using some other information by proxy on a per country basis to try and find effects based on differing tech levels available in different countries. Given as earth is tech-8 or so, based on manufacturing capability, and that tech can be purchased by any group that has the money to purchase it and pay for maintenance of it, then I may go with tech level is proportional to a country's GDP per capita. Trillion Credit Squadron uses GDP per capita based on a given tech level, so why not? I can then use population, agricultural workers and agricultural land to work out tech effects for production and labor per sq. km with respect to tech level... or at least enough, perhaps, to show a trend.

I figure that I'll need to add a bit to a new-improved spreadsheet for my world-building crap; a dumbed-down 1d energy balance model of surface temps to give a better idea of land lost to ice when things are too cold ( at least until I get my computer up, running and learn to use a gcm model I've found; 48 cores should keep me from waiting days to see a result ).

My overblown traveller-based projects continue to stagger drunkenly onwards...

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https://sites.google.com/site/moukotiger/home


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 Post subject: Re: pop related junk
PostPosted: Fri May 05, 2017 2:28 pm 
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Agemegos wrote:
Agemegos wrote:
At low tech levels where you don't have motorised agriculture a lot of your primary agricultural production has to be fed to traction animals for the ploughing, which reduces the effective carrying capacity.

To be explicit about "a lot", I have read that before the invention of steam trains two-thirds of the crops (including hay, grown in irrigated "meadows") were fed to draught animals. I guess that includes horse-drawn transport as well as the ploughing (which was far more significant), on the other hand it does not include vegetable oils and wood grown for lighting, cooking, and heating fuel.

That is, mechanising tillage and transport may have tripled the carrying capacity of some environments.


I think you also have to factor in that mechanisation drives the carrying capacity of rural areas down! (Carrying capacity isn't quite the right word - employment capacity?). A farming documentary interviewed a farmer who pointed out that in his grandfather's day, his farm required 50 people and a small army of horse to work the land. Today it takes 3 people and a small army of machinery to work that same land. So the rural population has crashed from 50 to 3.

The 'spare' 47 rural people might still all be living locally, but they've probably emigrated to a town.


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 Post subject: Re: pop related junk
PostPosted: Fri May 05, 2017 10:10 pm 
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That certainly makes a big difference to the settlement structure, but as far as I know ForeSight is the only SFRPG whose planet generator produced settlement structure. I think Ishmael is at present only concerned with the total population of a planet, and not with whereabouts the people live.

There has certainly been a strong trend in which increasing productivity of labour in agriculture has allowed (or driven) population from the countryside into towns, cities, megalopolises, and concordantly allowed (or driven) workforce into manufacturing and services. That goes all the way back to the replacement of spades and hoes with ploughs and harrows as horticulture turned to agriculture.

Extrapolating that trend into the SFnal future we get a vast hinterland of broad-acre solar-powered high-biotech energy-fixation and chemical synth industry cultivated almost entirely by robots, the great majority of the people living mostly in sharply-circumscribed extremely densely-settled cities that are enormously rich in public goods and social resources. If our nerve doesn't fail us we at least consider the possibility of such urbanisation occurring on an interstellar scale, as population drifts from the hick life on agricultural planets to the bright lights, rich social life, profuse infrastructure, and plentiful well-paid jobs on Trantor or Coruscant.

Against that you have the possibility that the trend might change. With improving transport technology (and/or, as Arthur C. Clarke suggested, communications) people might be able to enjoy what cities offer without having to live jam-packed to get it. Telepresence, teleoperation etc., or rapid easy commuting with no parking problem might allow cities to become less dense and less circumscribed, so the the trend to urban sprawling continues to the point of Frank Lloyd Wright's "disappearing city".

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— Brett Evill

My SFRPG setting, Flat Black

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 Post subject: Re: pop related junk
PostPosted: Fri May 05, 2017 10:22 pm 
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Ishmael wrote:
I only have a couple of data points to figure out how tech affects production per sq. km, or workers needed per sq. km., but I have to hope to work something out based on data from the site, http://www.nationmaster.com ( in my case, http://www.nationmaster.com/au ). Naturally, it won't give traveller tech info directly, so I'll have to work that out by using some other information by proxy on a per country basis to try and find effects based on differing tech levels available in different countries.

For what it's worth, the GURPS Space 4th ed planet generation sequence gives carrying capacity as a function of TL (and characteristics of the planet). I asked, but did not learn, what data it was based on.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts on SFRPG must not be reproduced beyond the board except with explicit permission from me.


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 Post subject: Re: pop related junk
PostPosted: Sat May 06, 2017 10:13 pm 
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The procedure for generating Carrying Capacity in the GURPS Space 4th ed world generation sequence is as follows:
  1. First you calculate the world's "Habitability", which depends on its atmosphere, hydrographics, and climate (temperature). I reckon that Earth is a 7. Then you add a "Resource Value Modifier", which for planets is about -2 to +2. For Earth we will guess +0. The sum is Affinity. Carrying capacity goes with 2^Affinity (rounded somewhat).
  2. Then you take a value off a table for tech levels
    Code:
    GURPS     Basic
     TL       Carrying capacity
      0           10 000     Stone Age
      1          100 000     Bronze Age (after ~3500 BC)
      2          500 000     Iron Age (after ~1200 BC)
      3          600 000     Mediaeval (after 600 AD)
      4          700 000     Age of Sail (after ~1450)
      5        2 500 000     Industrial Revolution (after ~1730)
      6        5 000 000     Mechanised Age (after ~1880)
      7        7 500 000     Nuclear Age (after ~1940)
      8       10 000 000     Digital Age (after ~1980)
      9       15 000 000     Microtech Age (after ?2025?)
     10       20 000 000     Robotic Age (after ?2075?)
    11+       no guidance    Age of exotic matter and later

  3. And you multiply. Current Earth (Affinity 7, TL8) comes out to 2.5 billion.
  4. Then you multiply by the square of the world's diameter in Earth diameters.

It's interesting that GURPS considers Earth at present to be overpopulated by a factor of three at current TL and by a factor of two for the coming tech level. Either they figure that our current agricultural production is grossly unsustainable, depending on the rapid depletion of phosphate and fossil fuels, or they figure that Earth has a positive Resource Value that they didn't mention.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts on SFRPG must not be reproduced beyond the board except with explicit permission from me.


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