Fog of War
Fog of War is the game mechanic in which a player's access to information is limited to the region of map which is currently revealed by his units, buildings, and abilities. It is represented by dark and light regions on both the minimap and the main screen.
At the beginning of a game all terrain and the location of mineral patches, vespene gas geysers, and Xel'Naga Towers is revealed to the player.
As a player's units move about the map they grant full vision to the player within the vision range of that unit. This is shown on the minimap and the main screen as a fully lit region. Any units or structures within that area will be displayed on the main screen and also on the minimap as colored dots.
When a player loses sight of an area, either by a unit moving away or dying, the map area reverts to a darker shade and any information about units is removed from the main screen and the minimap. Buildings will still be shown at their last known location in their last known state. This includes structures which are being built, burning down, or are later destroyed but does not include lifted or uprooted buildings. However, the player will not be able to select these buildings through the Fog of War. This means he cannot ascertain the health of any structure, identity of a building structure, or any other information not graphically represented on the main screen.
In the special circumstance that a player's unit is killed by an enemy unit of which the player does not have vision, the player will be briefly granted vision of the opposing unit. However the vision granted is not full vision in the sense that it cannot be used for units to attack. This is most notable in TvT battles between Siege Tanks, whose attack range exceeds their vision range.
It is not possible to see the shadow of a unit that is hidden in the Fog of War, even if the shadow would be cast into vision range.