Features are elements of terrain or vegetation that appear in a hex, atop the hex's terrain. Think of these as modifiers for the base tile underneath. Features modify a hex's productivity and might also alter the amount of Movement Points (MPs) a unit expends when entering the hex. Features may also provide defensive combat bonuses or penalties to a unit occupying the hex.
Flood Plain
Flood plains are low-lying areas adjacent to rivers. Each year, the river floods, thus providing natural irrigation and rich nutrients to the adjacent land. This makes flood plains fertile and the most productive farmland possible.
If you're looking for a high-growth city, settle along flood plains, and reap the benefits of large Food bonuses. Compound this with buildings that generate Food and internal trade routes, as well. This catapults your new city into a higher population and helps it start producing better buildings and more resources much sooner than it would otherwise.
- Food: 2
- Production: 0
- Energy: 0
- Combat Modifiers: -10%
- Movement Cost: Food0
- Food1
Forest
On Old Earth, forests were a great source of bounty, providing wood for fire, tools, and shelter, as well as homes to many animals used for sustenance and clothing through the ages. While not as critical for survival on this planet, native forests still supply Food and raw materials for Production.
If you think that your territory is safe from invasion, cut down forests for the temporary bonus to Production. When enemies are close, it's wiser to leave forests standing and deploy melee units in them to exploit their defensive advantages.
- Food: 1
- Production: 1
- Energy: 0
- Combat Modifiers: +25%
- Movement Cost: Food0
Tiles with forests covering them always yield 1 Food and 1 Production, regardless of the underlying terrain type.
Ice
Ice is just ice, and it's almost entirely useless to civilization. It is impassable (except to air and hover units) and provides no benefits.
- Food: 0
- Production: 0
- Energy: 0
- Combat Modifiers: None
- Movement Cost: Food0
- Food1
Marsh
Although rich in biodiversity, marshes have little to offer a growing colony. You can drain or farm marshes to increase their yield, but they are difficult to move through. Note that military units in marshes receive a significant penalty when attacked.
Avoid settling near marshland unless you have a surplus of workers ready to develop that area. If you have the workers to spare, go ahead and rush through these tiles to make them more productive for your city.
- Food: -1
- Production: 0
- Energy: 0
- Combat Modifiers: -15%
- Movement Cost: Food0
Miasma
Miasma is a terrain feature that can coexist with any other feature and on any type of terrain except snow and ocean. This is an "infestation" of the tile with virulent spores that are actively hazardous to humans and their machines until the spores are removed or certain Technology is adopted.
Any unit that ends its move on a tile with miasma suffers 10% of their maximum Health in damage. Workers get Technology to protect themselves fairly early on, making it safer for them to stop and develop terrain with miasma. Other units must develop far into the right side of the tech web to remove this problem. (The right side of the tech web is where you find many of the Harmony Technologies).
- Food: 0
- Production: 0
- Energy: 0
- Combat Modifiers: None
- Movement Cost: Food0
- Food1
Rivers
Traditionally, cities have been built along rivers, and for good reason. Rivers provide irrigation, improving the farmland around the city. They also serve to protect a city, as it is difficult to mount an assault against a city across a river.
Rivers run along the sides of the tiles rather than through them, so rivers provide their benefits to all tiles/units adjacent to them. They grant +1 Energy to all adjacent tiles.
When attacking across a river, the attacking unit gets a 20% penalty to its Combat Strength. Units use all of their remaining Movement Points when crossing a river. There is, however, no additional cost for crossing a river if a road or magrail passes over the river.
Michael Note: Currently roads/magrails do not prevent this penalty. I suspect that's a bug rather than a feature. Please remove the above text later if rivers still stop movement even while bridged.