Just like S.T.A.L.K.E.R and Fallout, Dark Researchers is going to be an open world, survival game, based on exploration and stealth. People who have worked using the Source engine may have noticed that it isn't really made for open world games, as the hammer editor itself has many limitations concerning the map's file size or the detail sprite count. These limitations do not really help in making such games though with the right optimisation everything (or at least what we want to achieve) is possible.
That's also the main reason why we haven't released any actual screenshots of outside areas which occupy most of the game's space. Most of the maps are really large and still need to be worked on in order to take a complete screenshot including the skybox etc.
Another aspect that should be taken into consideration are entities such as NPC's, weapons and vehicles. We need to modify the map's size so vehicles have space to move in both air and land.
That's it. Just a brief article about the game's maps :P
Good luck to optimize them :D
I already feel my PC lags :D