Friday, January 15, 2021

How much room is there on a planet?

Talavera, the capital of the Empire of my Church and Empire setting, is a large planet with vast oceans. The UPP is A-969835-F, and 947 million people. But how much room do they actually have for a billion people?

Size 9: 9,000 mile diameter

Hydro 9: 90% of the planet is oceans

I had an initial idea of a densely populated island, where the buildings reach high into the sky to make room for nearly a billion people.

Then I did some math. What I found was, to say the least, not that dramatic.

Talavera has 25,446,900 square miles of land area. Spread 947,000,000 people over that and you get a population density of 37.215 ppl/mi^2.

According to this table of population densities of countries, that's less than Norway or Sweden. Neither are the sorts of places you think of when you think of dense populations. China, at 378 ppl/mi^2 is ten times denser. 25 million square miles is several times the size of Russia.

I did up a table to compute the square miles of surface area on planets in Traveller. By taking the Size code and cross-referencing with the Hydrographics code, you can find the land area of any planet of normal parameters. It may be water, it may be ice, it can be some other kind of liquid.

Here is a sample of the table, including a few Earth examples for comparison. The entire table, in MS Excel format, is available here.  The long and short of it is this: any planet is going to have plenty of room for exploration, or to hide something or someone. Even a Size-2 planet with Hydro-5 has space near to the size of Russia to work with.

Of this area, only a scant percentage is going to be inhabited, unless A) the population is in the Billions or above and B) most of the planet is covered by liquid or ice. A planet with only a few million people is going to be 90+% uninhabited.

What might go on in the frontier areas of a lightly populated world? Possibly a lot.  Share your ideas in the comments.
Size Code Diameter Radius Total Area Hydrographic-5
0 500.0 250.0 785,398.2 392,699.1
1 1,000.0 500.0 3,141,592.7 1,570,796.4
2 2,000.0 1,000.0 12,566,370.8 6,283,185.4
3 3,000.0 1,500.0 28,274,334.3 14,137,167.2
4 4,000.0 2,000.0 50,265,483.2 25,132,741.6
5 5,000.0 2,500.0 78,539,817.5 39,269,908.8
6 6,000.0 3,000.0 113,097,337.2 56,548,668.6
7 7,000.0 3,500.0 153,938,042.3 76,969,021.2
8 8,000.0 4,000.0 201,061,932.8 100,530,966.4
9 9,000.0 4,500.0 254,469,008.7 127,234,504.4
10 (A) 10,000.0 5,000.0 314,159,270.0 157,079,635.0










New York



  1. It's easy to forget the scale planets are. Our minds don't do proportions at that scale very well.

  2. Reminds me of a thread at COTI several years back. The OP was struggling to explain an agro exporting world with a widespread smallish population and a pre-gravitic tech level. The population wasn't large enough to construct or maintain the extensive rail or road networks the OP felt was needed and the planet's hydrographic rating of 2 was "obviously" too small to take up the slack.

    I pointed out that the Atlantic and Indian oceans each cover about 20% of Earth's surface so you could have regions separated as much as Durban and Perth or London and Montevideo connected by maritime networks at relatively low tech levels. Using "only" river, coastal, and oceanic shipping, Colonial and Federal Era America produced, gathered, and shipped millions of tons of ag products to Europe. In 1794, a single grain convoy of over 300 ships sailed between Chesapeake Bay and France triggering a the 4th Battle of Ushant when the UK attempted to intercept it.

  3. Bear in mind though that not all the land might be habitable. If you look at a population map of Australia, for example, it looks less like a continent and more like an archipelago - a relatively densely-populated one.

    For example, might a planet which is 90% water not have more storms? Wouldn't everything be coastal? Perhaps the people live in a few cities surrounded by huge walls against storms..

    Even if it's all habitable, it might not all be inhabited, either. Perhaps the local authorities like to have vast swathes of forest, like feudal lords.

    1. Very true. Among the many subjects I've studied outside of classes to apply to Traveller, human geography is one of the more interesting. Why do people live where they do? If they have any choice, people will live on level ground where they have access to food and water, and transportation routes. Hard to do in the Dakota Badlands, for example. Thank you for pointing it out!