Alpha Centauri Wiki
The first order of business after Planetfall was to secure a food supply. Few native life forms were edible without extensive processing, so wide tracts of land were turned over to Earth-style agriculture.

Terraforming refers to the actions your formers can carry out to improve the terrain around your bases and their productivity. Formers can also be used offensively, in a way, to bridge landmasses using the raise terrain command, isolate enemies by lowering it, or creating mountains to reduce rainfall: Mountains 2000m above sea level and higher significantly affect cloud formation and rainfall by trapping the moisture being carried by the prevailing wind. Basically this means that areas "downwind" (in this game, "east", or "right") of a mountain will be dryer, and areas "upwind" of a mountain ("west", or "left") will be wetter as moisture is trapped to their benefit. You can take advantage of this phenomenon by having your Formers raise mountains to "dry out" your downwind opponents or to increase rainfall for your upwind bases.

Land improvements[ | ]

Improvement Effect Turn Prerequisite
+1 nutrients in a land square 4
+1 nutrients in a land square with a farm (+2 total) 8
+1 in flat and rolling land squares
+2 in rocky
+3 in rocky squares with roads
+1 in areas with minerals resources
+1 energy per 1000m of elevation 4
Produces 1 nutrients and energy and 2 minerals 4
Reduces movement costs for land units by 2/3 1
Units move at no cost through mag tubes 3
+50% defense for stationed units 5
Air units can land at airbases to repair and refuel 10
Detects enemy units in a two square radius
Defending friendlies in that area gain +25% to defense
Raises rainfall levels in surrounding squares by one full grade
Produces +1 nutrients in own square and stacks with a farm
+1 energy collected in surrounding squares
Doubles as a solar collector
Echelon mirrors do not affect one another
+6 energy and minerals per borehole
Cannot produce nutrients
Cannot be built on slopes
Produces 2 nutrients, minerals, and energy
Upgrades military units by one full morale level (once)
Cannot be built

Sea improvements[ | ]

Improvement Effect Turn Prerequisite
+2 nutrients in a sea square 4
+1 minerals in a sea square (+2 with Advanced Ecological Engineering) 8
+3 energy in a sea square 4

Orders[ | ]

Improvement Effect Turn Prerequisite
Aquifier Creates new river from point of drilling to the coast 18
Raise Increases altitude by 1000m
Can be used to raise sea floor and create dry land
Lower Reduces altitude of target area by 1000m
Can be used to deepen the sea floor
Level terrain Reduces rockiness of a square 8
Remove fungus Removes xenofungus 6
Plant fungus Cultivates xenofungus in target square 6