The sight range (or sight radius) of a unit means that it can keep a number of tiles around its current location under "observation." This is achieved by lifting the fog of war from the tiles which are being "observed." Thus, all activity in these tiles will be visible to the unit's owner (and sometimes its allies).
Line of sightEdit
Note that sight can be obstructed by elevated terrain and certain features, namely Hills, Woods, Rainforests, and Mountains. The presence of these features within the unit's sight radius will create obstacles, which will affect visibility of certain tiles; when related to the current position of the unit we say that it has (or doesn't have) "line of sight" to these tiles. Visibility follows these rules:
- A unit always sees tiles immediately adjacent to the tile it occupies; it follows that line-of-sight rules only apply to the tiles 2 or further removed from its current position.
- An obstacle will hide the tile behind it which forms a direct line from the unit's position.
- An obstacle will also hide tiles found to the left and right (or up and down) of the direct-line tile (as per the hexagonal tile system); note that this is often overlooked as one or both of these tiles may still be revealed from being unobstructed on the other vectors of the unit's sight!
- Sight is also affected by elevation. In other words, some features are taller than others, and may become visible under the following circumstances:
- Hills form a "second level" as far as visibility is concerned. Mountains, as well as Woods and Rainforests found on top of Hills, form a "third level."
- Features only block visibility on tiles if these are on the same level as the blocking feature. If they are one level above it, they become visible. For example, let us assume the unit is on flat terrain, and there is a Hill blocking its sight. If the tile directly behind the Hill is another Hill, it will be hidden (being on the same, second level); if, however, it is a Hill with Woods on it, or a Mountain, it will be visible (being on the third level).
City Centers, Encampments, and most units with ranged attacks must have line-of-sight to a target in order to attack it. Late-game units such as Artillery and Battleships, however, can lob their shots, allowing them to attack any target within range as long as the tile is visible in any other way.
Units may overcome most line-of-sight obstacles if they stand on a vantage point - a tall feature which will allow the unit to see above obstacles.
- A unit situated on a Hill gains a vantage point and will be able to see over all terrain, unless blocked by a third level feature, such as Mountains or Hills with Woods or Rainforests on them.
- A tile with a feature which is one visibility level above the tile immediately in front of it will become visible to a unit, even if it is 1 tile outside its usual sight range. For example, a unit with a sight range of 2 may still see a Hill or a Mountain three tiles away. A Mountain three tiles away will still be visible even if there is a Hill between it and the unit; however, if there is Woods or Rainforest on the hill, the Mountain behind won't be visible (because it is on the same level).
- City Centers and Encampments will provide a vantage point to ranged units in their tile, even though their own ranged attack won't have vantage!
Most land and naval units have a sight range of 2, meaning that they can "see" up to 2 tiles away from their current position. Settlers and certain naval units are an exception and have a sight range of 3 - this helps them better explore the world. Use the Settler's sight range to choose better spots for settling; use the other units' extended sight to better execute reconnaissance missions and reveal more terrain with less movement.
There are a few ways to increase the sight radii of units:
- Spyglass, a Tier III Promotion for recon units, increases a unit's sight radius by 1.
- Rutter, a Tier II promotion for naval melee units, increases a unit's sight radius by 1.
- Observation, a Tier III promotion for naval raider units, increases a unit's sight radius by 1.
- Scout Planes, a Tier I promotion for naval carrier units, increases a unit's sight radius by 1.
Also, the Sentry promotion for recon units allows them to ignore Woods and Rainforests in their line of sight, greatly increasing visibility in most circumstances.