To make an outdoor City with buildings you can also enter.
Personally I use the FPSC editor utilising the pograms own level building features to build almost all buildings the player has any access to in any way. i.e. build with segments.
For buildings or other elements that are on the extremeities e.g. the outskirts of the level - that have liitle or no interaction with the player nor any particular direct main view to the camera then Its fine to use any .x file model entity you may make externally in a model editor as a one piece building for instance.
The reason for this is default editor segment type created buildings are in theory at least but not wholly in practice due to compile or other engine issues - able to block the view and thus reduce ploy counts and help keep fps acceptable in outside levels.
Entity type structures on the other hand even if placed as static entities in my experience do not block the camera view and as a result on compile and game run the engine can see straight through them increasing ploy counts to view dramatically. Thas what happens at least in my own outdoor levels.
The morale therefore is you can use models for high skyscrapers and such but always keep them in the distance being the last object before the world boundary with other buildings in front of them to block the view at all times - try not even place them at the boundary if there is nothing solid behind or in front of them as the engine may see straight through them to infinity and beyond as it were - tracing through them and around the level returning high poly counts. Just as the engine can can see around corners in ceratin instances when it should not. Effectively these are what inside FPSC one might describe as instances of level leaks.
I would suggest always place a solid fence or wall or something at ground level in front of any entity building at the very least - this will help in blocking the view from the engine.
Much more experimentation is required in Outdoor level building to find the best methods of optimisation - after we see what any update to FPSC brings and if issues such as those mentioned get fixed, stay the same or become worse.
Your guess is as good as mine.
I am personally presuming at this stage that the status quo will remain as is and there wont be any improvement so if you need to build a City it might be best just to get on and do it rather than waiting.
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