Saturday, December 01, 2012

Top-Down RPG World Design, Part I: Planet, Continents

This is Part I of hopefully a lengthy series, posted as I graduate to new levels or sections, of a top-down method of creating a game world, starting at the "top" - the celestial body itself. I'll be using Earth and our solar system as my base examples, so let me put its stats up first.

PLANETDIA (MI)SqMiLand%Land SqMiNumCont

Now, looking at the other planets in just our solar system, I find that they range in diameter from 3,000 to 90,000 miles in diameter. I'll also include the relatively new classification of "dwarf planets", of which Pluto is now a member; these range from 600 to 1,600 miles in diameter. So overall, the planets and "planetoids" in our solar system range from 600 to 90,000 miles in diameter.

After extrapolating both directions from the above averages, I arrived at a fairly consistent chart for random dice determination for new planets. You could either use the 3d6 roll to see which type of planet you're making, or just choose whatever strikes your fancy.

1. Planet Size and Type

3-4Dwarf 200 + 3d6 x100500-2000Pluto, Ceres, Eris
5-9Small 1000 + 3d6 x5002500 to 10,000Earth
10-13Medium 8000 + 3d6 x100011,000 to 26,000

14-16Large 24,000 + 3d6 x100027,000 to 42,000Neptune, Uranus
17Giant 35,000 + 3d6 x300044,000 to 89,000Saturn, Jupiter
18Super Giant2,000 + 3d6 x600090,000 to 180,000TrES-4b

2. Total Planetary Area (Square Miles)
Multiply the planet's diameter (in square miles) by itself (in other words, square it), then multiply that result by Pi (3.1416). So the formula is:

Total Planetary Area Formula: Planet Diameter^2 x 3.1416 (Diameter x Diameter x 3.1416)

The Earth example is:

7,930 x 7,930 = 62,885,000 x 3.1416 = 197,560,000 square miles

3. Land/Water Ratio
Use the below chart to either choose or randomly determine what percent of your planet is land. The remaining percent is of course, water.

Total Planetary Land
Multiply your Total Planetary Area by your Land% (40 = 0.40) to get the actual square miles of land of Total Planetary Land.

2d6 x5Land%World Type
240 Aquatic
345 Near-Aquatic
450 Very Wet
555 Wet
660 Tropical
765 Near-Tropical
870 Earthlike/Temperate
975 Dry
1080 Arid
1185 Near-Desert
1290 Desert

4. Continental Area (Square Miles)
Now we'll determine both the number of continents on your planet, and their area in square miles.

Smallest Continent Area
We will start by determining the size of your smallest continent, by multiplying your Total Planetary Land by 5% (0.05). This constitutes the minimum square mile criteria required for a landmass to be considered a continent. If you generate any area of land roughly this size, it likely signifies you have determined your last continent.

Largest Continent Area

Make the roll indicated below and multiply it by your Total Planetary Land to determine your largest continent's area in square miles.

Continental Area Percent Formula: 15 + 2d6 x5 (yields 25-75% or 0.25-0.75)
Second and Additional Continent Areas
For your additional continents, subtract the largest continent's area from the Total Planetary Land to get your Remaining Land Area. Make a second Continental Area Percent Formula roll, multiplying the result by your Remaining Land Area to get your new Remaining Land Area.

Do this, multiplying your new Continental Area Percent by the most recent square miles of your Remaining Land Area, until your Remaining Land Area is approximately equal to your Smallest Continent Area, at which point you assign this last area of land as your last continent. You should wind up with somewhere between 4 and 16 continents, depending on planet diameter and total land area values.

Next: Now What? Maps and Continents

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