Since I installed fsx my test flight after any config changes has been to take off from London city airport EGLC and fly west over the millennium dome, along the Thames to heathrow.
The frame rate always takes a hit after takeoff which I attributed to the scene complexity with the dome and canary wharf sky scrapers. The power of association! However examining the scene in the intel fpa tool showed this was nonsense. The dome is a single drawcall, which is no more cost than fsx spends drawing a couple of trees somewhere near fulham broadway.
I used system internals process explorer to watch what happened. As the frame rate slows there in indeed a big spike in disk reads. Drilling down in the tool I could see airport bgl files for LosAngeles and malmo?
So I read the sdk! It explains that traffic is implanted in a block of 9 squares surrounding the aircraft and these are at the equator approx 60 miles square each. Clearly then they must be based on degrees of latitude and longitude
There is one other place of interest near to the dome! Greenwich “home of the prime meridian”.
So the slow down has nothing to do with the London scenery, it’s fsx implementing traffic for the next three squares located 2 degrees west. That includes Southampton, Birmingham and some other midland airports.