Rise of Nations Wiki

Scouts have a large line of sight.

Line of Sight is a game concept that determines how far a unit or building can see. Line of sight is shown by the brightest areas of the map. Areas that are visible but appear darker than the rest of the map show areas that have been explored but are not currently being observed (see Fog of War). Enemy units outside a nation's line of sight are hidden from view, while enemy buildings remain visible once they have been discovered. Science Science Research Icon.png level 7 will extend a nation's line of sight to their entire territory. The Space Program wonder reveals all units, buildings, and terrain on the map, even those belonging to enemies. 

Allied LOS[]

With Science Research Icon.png Science level 2, a player will be able to see their ally's line of sight. Note that this only applies to diplomacy-related game modes, as team mates in modes using fixed teams will always share line of sight regardless of technology level.

This is very useful as any reconnaissance completed by allies will also be visible to the player, and military engagements can be coordinated far more easily. This setting can be disabled if using custom rules.