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 PP).
 * Otherwise you have to build a much more expensive Colony Ship (500 PP). You may even build a Colony Ship for a planet in a system you already occupy if there's a good reason for wanting to found the new colony faster than your colony in that system can build a Colony Base, for example if the planet has gem deposits.

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 - it might be better to concentrate on something else, such as research or on growing the population of your existing colonies or on improving their population capacity, research or industrial capabilities, profitability or, if your race is not Lithovore, their fertility.

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.

At some point you will have to stop colonizing anyway, for example because it would be difficult to defend new colonies far away from established colonies that could build warships to protect them.

This page only deals with colonization in the early, low-tech stage of the game. Later you should generally "colonize" by invading other empire's colonies. In this mid-game stage there may be a few uncolonized planets behind the expanding boundary of your empire, and you may wish to colonize more "difficult" planets because you now have technology and money to make them useful in reasonable time. But this guide cannot anticipate how the mid-game will develop, especially which technologies you will research at this stage.

Population
Population is power. So 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 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.

Minimum useful sizes
Usually it's not worth colonizing planets whose initial maximum population  for your race is less than 4:
 * In the early game you're short of cash - even you've chosen a race design with advantages in money, e.g. with a Democratic government, because cash races are usually not strong producers and have to use the "buy when half-built" technique a lot.
 * To help pay for the maintenance of buildngs on the planet, you'll generally want to build a Spaceport. But on planets with normal maintenance costs Spaceports only make a profit if the population is at least 4; and on Toxic, Radiated and Desert planets maintenance costs are higher, so the break-even population for a Spaceport is higher.
 * When you build Biospheres at a colony, its maximum population will increase by 2. But Biospheres have a maintenance cost of 1 BC per turn. Ideally you should build a Spaceport before Biospheres, to pay for the Biospheres.

Size affects pollution
A planet's size also affect show fast it can build, because pollution starts to bite at lower production levels on smaller planets. Note the words "planet's size" - the point at which pollution bites is determined by the planet's physical size (Time / Small / Medium / Large / Huge) and by population capacity increases produced by terraforming, but not by racial advantages in population capacity (Subterranean and, on "wet" planets, Aquatic). Of cours epollution i snot aconstraint for Tolerant races.

Population 1 housing colonies
There's one important exception to all of this: if you have a few planets with maximum populations of 8 or more (for your race), you could colonize a smaller planet to use it as a Population 1 housing colony. The smaller planet should ideally be one that can easily be terraformed to a useful size later.

Food
Food production is not a constraint for Lithovores in the early game; but even they should try to colonize planets that are good for farming, so that they can later support non-Lithovore populations that they have conquered.

Depending on the type of planet, your colonists can produce 0, 1, 2 or 3 food per farmer (3 only for Aquatics on "wet" planets and for on-Aquatics on the very rare Gaia planets). Non-Lithovores would obviously prefer to colonise planets where each farmer can produce 2 or 3 food in the early game - once again this depends on your race design: Unification governments and, on "wet" planets, Aquatic races can produce more food. Colonizing a lot of planets that need to import food will harm your economy in a number of ways, whose combined effect is serious in the early game:
 * Your better planets need to do more farming, which diverts colonists form research and production.
 * You have to build more Freighters, when you'd probably prefer to build something else or to stockpile production.
 * Each Freighter costs 0.5 BC per turn that it is in use.

Low-fertility planets should generally be used only as Population 1 housing colonies - preferably sending people to other colonies in the same system, to avoid the costs of using Freighters.

If you have a choice of 2 low-fertility planets, colonize the one that will terraform directly to to a reasonably fertile planet (for your race) later.