Master of Orion II: Battle at Antares/Which planets to colonize

There are 2 ways to create new colonies:
 * If there's an unoccupied planet in a system where you already have a colony, your colony can build a Colony Base (200 construction points; think of it as a very short-range spaceship).
 * Otherwise you have to build a much more expensive Colony Ship (500 construction points).

In the early game even a Colony Base is a significant construction project, so you need to decide what you hope to gain from each colony, and whether the gain justifies the cost.

What types of planet are good for what
This is quite complicated because:
 * A few planets have special features that make them unusually desirable, even if you wouldn't want a similar planet without the special feature.
 * Some racial traits affect the desirability of planets. For example a Medium Ocean planet has an initial maximum population of 4 for a "standard" race, but a maximum of 16 for an Aquatic race, which also gets a farming bonus there.
 * Most planets can be terraformed when you get the technology (it's the only one at that level, so even an Uncreative race can research Terraforming if it wants to). So you may want to consider how easily a planet can be terraformed into a "good" planet for your race; and how to use it in the meantime.

Good players know all the possibilities and do this analysis without conscious thought. If you're a newcomer to ''MOO II', don't get discouraged by the apparent complexity of all this - after 10-20 games you won't notice yourself thinking it all out.

Planet maximum populations
The game software will show a planet's maximum population when you run your mouse over the planet's icon in various screens:
 * If the planet is empty, it shows the maximum if colonized by your race.
 * Otherwise it shows the maximum for the race that currently occupies it.

But as you get used to the game you will find yourself thinking of how the less hospitable types of planet can be improved, so you'll want to know in advance what the planet's maximum population will be if you upgrade it. The following table shows the maximum populations of each size and type of planets for each of "normal", Aquatic, Tolerant and Subterranean races (if you use combinations such as Aquatic + Tolerant you'll have to get used to working them out yourself):

Costs of Terraforming and Gaia Transformation
The main rules are simple and you can easily work out the costs of upgrading a any planet to any other possible type:
 * Toxic planets cannot be improved.
 * Radiated planets cannot be improved until you have built a Radiation Shield (or one of the advanced versions of Radiation Shield), which converts the planet to Barren.
 * Terraforming cannot produce Ocean or Gaia planets. The results of 1 terraforming project are:
 * Barren planets become Desert if in the 2 inner orbits nearest the star, Tundra if in the 2 outer orbits furthest from the star, and either Desert or Tundra (random, 50% probability for each) if in the middle orbit. Tundra becomes Swamp; Desert becomes Arid; Ocean, Swamp and Arid become Terran.
 * A planet's first Terraforming project costs 250 construction, its second costs 500 and its 3rd costs 750.
 * Gaia Transformation converts Terran planets to Gaia, at a cost of 500 construction points.

It's easy to work out that the greatest increases in maximum population from a single terraform (250 construction points) are Ocean to Terran (except that Aquatic races gain nothing), Swamp to Terran (but Aquatics gain the least) and Desert to Arid; and that terraforming Barren planets only provides an immediate benefit to Aquatics, and even then only if the result is Tundra. These are probably the only terraforming possiblities you should consider when deciding whether to colonize a planet, since second and third terraforming projects on the same planet are expensive.

If you are considering terraforming mainly to improve farming productivity, think first about:
 * Soil Enrichment, which costs only 120 construction points; but is not possible on Barren, Radiated or Toxic planets.
 * Importing food from a more fertile planet. A freighter fleet costs only 50 construction points.

Population
Population is power, up to a point - and this page should help you to decide where that point is.

Ideally you want mainly planets that have a large maximum population or can easily be terraformed to a large maximum population. But the maximum population partly depends on your race design - Subterranean and Tolerant races get higher than normal maximum populations on all planets; Aquatic races get higher than normal maximum populations on "wet" planets. Fortunately the game software helps by showing a planet's higher maximum population when you run your mouse over the planet's icon in various screens:
 * If the planet is empty, it shows the maximum if colonized by your race.
 * Otherwise it shows the maximum for the race that currently occupies it.

And you may decide to build a Colony Ship even though you already have a colony in the target system, for example if the colony is small or mineral-poor and the planet where you'd build the Colony Ship has much greater industrial capacity.