Tag Archives: Subsector

Creating Local Space (1)

While I am working on the framework to generate the low-level detail, I can’t help myself but to work on the larger picture – and some actual setting data. Keep in mind that I already created one sector last year; I consider it my “draft”, and it will certainly inform many of the decisions I will be making.

For the first sector, I simply created a small grid of 3×3 sectors with a rough drawing of what I thought local space should look like. (In reality, these should be rectangular.)


I’ve refined this method somewhat. I created the following in The GIMP:


Black are “sparse” or “rift” regions, white are regions of greater star density,

The process to create such an image is fairly simple:

  1. Create a new image. I used landscape, A4 size. But this doesn’t matter.
  2. Filters -> Render -> Clouds -> Plasma.  I used the maximum Turbulence.
  3. Colors -> Desaturate
  4. Colors -> Threshold. Play with the sliders until it looks nice
  5. Filters -> Blur -> Gaussian Blur. I used Blur method “ILR” and radius 30×30, though you may have to change this depending on your image. You want to significantly soften the edges, while keeping the general shapes recognizable.
  6. Create a second layer.
  7. On the second layer: Filter -> Render -> Clouds -> Solid Noise. I used detail 15, x and y size of 16, and both Turbulent and Tilable disabled.
  8. Move this new layer underneath the original layer.
  9. Set the original layer’s mode to “multiply”.
  10. Merge the layer down.
  11. User Colors-> Threshold, play with the sliders again until you get nice distribution.
  12. If you dislike the results, try inverting colors or different random seeds for your plasma clouds.
  13. Don’t be afraid to manually edit the image after step 11 – I did!

Placing our Sector

Note that the image doesn’t have any sort of scale, which gives us some flexibility. I used Inkscape to place the same 3×3 sector grid, and I resized it a few times until I had the “right” fit. I decided on this location:


As is the tradition, X marks the spot – the sector of my setting. I picked this location because there is a lot of “interesting geography” adjacent to it.

Here’s the zoomed section, with subsectors stenciled in as well:


Looking at the map, I think that these are good probabilities:


I estimate a total of 236 systems for this, or just over half the number of systems in my draft sector. If this ends up feeling too sparse, I can obviously shift the probabilities up a bit.

We’ll do that next time.

Subsector Trial Run 0

Here’s the data I rolled up for a sample subsector. I’ve set the world name to the temperature range. I used 5 or less for the system probability, just so it’s not too empty. Government, Law, TL, Starport and trade classifications are still missing.

Cold        0102 887600-0
Temperate   0106 7a1800-0
Temperate   0107 564800-0
Hot         0109 400500-0
Cold        0210 7a2500-0
Temperate   0201 621900-0
Frozen      0203 ba6000-0
Temperate   0205 ab9900-0
Cold        0209 9c4200-0
Roasting    0306 a99500-0
Special     0401 ce7200-0
Temperate   0403 785700-0
Temperate   0405 779700-0
Special     0409 bf7200-0
Hot         0501 545400-0
Special     0610 cf4000-0
Roasting    0603 7a6700-0
Special     0604 8d6400-0
Frozen      0607 400000-0
Hot         0710 899100-0
Searing     0709 bc6100-0
Special     0801 8da700-0
Temperate   0803 874100-0
Frozen      0808 8b0400-0
Temperate   0809 673500-0

Using Alex Schröder’s Subsector map program shows us this layout (the colored markings are my addition, see below):



I know this is hardly statistically significant data, but still:

  • All worlds are fairly sizable. There are two main worlds of size 4, one of size 5.
  • Large size means weird atmospheres, hence the “special” temperatures.
  • Almost all worlds are inhabited; Worlds in hexes 203, 610 and 607 are uninhabited.
  • Highest pop is 9 (“billions”) on worlds 201 and 205. 201 is a medium sized world with a thin atmosphere and little water. 205 a high-gravity 90% water world with a corrosive atmosphere, so they must have rolled 12 for population.
  • Two worlds have a population of 8 (“hundreds of millions”), and four have a population of 7 (“tens of million”). Total subsector population is thus <20 billion people. By chance, they are all clustered in the upper section of the map (see blue markings on the map, above) which gives us a nice division – this is obviously a frontier subsector with a few older, more mature colonies… works for me.

I wonder if I over-compensated on world size, but it seems like a reasonable mix of worlds to me.


When I first started working on the science fiction setting, I created several maps covering the Orion Spur and even the Milky Way galaxy. I quickly worked out that these settings were much too big for me to handle, even if I only worked on selected “important” systems.

I was in the process of working out the “correct” size out when Realmwright finally convinced me to watch Firefly – I had been hesitant because I knew that it had been cancelled. I was surprised how much Firefly “felt” like a Traveller game. More importantly, it made me think how important recurring characters and locations are, and I finally decided to bring the setting all the way down to the very small scale of a Traveller sector. (This was, incidentally, when I began using Traveller to model the setting.)

I ended up creating an entire sector, but I did not really think about the process first and found out, later, that it was flawed – one of the key lessons that led me to the creation of Contact Light.

How “big” is a sector really?

Obviously, a Traveller sector consists of 4×4 subsectors, each measuring 8×10 parsecs. But 36×40 parsecs doesn’t actually tell us much about the scale of a setting.

Travel times: Once I had decided on using a Traveller sector for my setting, I worked out that a constant-speed hyperdrive with a velocity of 0.5 parsecs would be ideal. A subsector is 14 hexes across (diagonally), so that means 28 days – four weeks. For comparison, it took Colonial Age settlers four to five weeks to cross the Atlantic ocean.

Number of systems: As it turns out, a Traveller sector is quite a crowded place. The Mongoose basic rules book recommends a 50% system density (and if memory serves me right this has always been more or less standard). Since a subsector has 80 hexes, this means forty worlds per subsector or 640 worlds per sector. That’s a lot. Incidentally, my current Sector contains 424 worlds – some subsectors are more sparse – and that feels overwhelming.

What’s “realistic”?

The stellar density near our solar system is 0.004 stars per cubic lightyear, or about 0.14 stars per cubic parsec. The nearest we can get with one or two dice is a 1-in-6, or  16.67%, chance. This would result in ~ 13 systems for a subsector, or 208 in a sector. (Anecdotal data: The Sol sector in Traveller contains 18 systems.)

What can we do with 2d6?

In reality, I can’t imagine why anybody would want to roll even 80 hexes manually, but let’s still stick to the dice conventions. So what can we actually do with 2d6? This quite easily calculated, too:




Per Subsector

Per Sector

2 or less





3 or less





4 or less


Near Earth



5 or less







6 or less








7 or less








In other words, my sector worked out spot on at the 33% mark, or twice the stellar density near our Earth.

And I frankly can’t imagine what a sector at 58% or higher will look like. Messy, for sure.

What’s “good”?

I don’t think there’s a single number you can cite and say “this is what you should use”, since it’s too intimately tied to other assumptions in your setting.

Looking at these numbers and at my first sector, I have a gut feeling that 27.78% is the sweet spot for what I have in mind. But as we noted, it’s not only the number of systems that matters, but how interesting they are; let’s keep the numbers in mind and revisit them when we’re further along in the world generation system.