All of the terrain throughout the campaign is essentially composed of three areas, with different sectors for Away missions and other such levels; upon progression, previous maps simply expand and the player's original bases from past levels are maintained. Also, its resource system is quite different from mainstream RTS games; Oil Derricks are established over specific, scarce locations which constantly provide a slow, fixed rate of income. Combined with a mission time limit, this resource method makes it generally infeasible for players to utilize certain traditional RTS tactics such as "turtling" (fortifying one or more bases against enemy attack, while stockpiling resources with which to produce a massive army).