Btw you can also move slowly by halving or quartering the sim rate. (Bind Increase Sim Rate / Decrease Sim Rate in options). Each decrease halves the sim rate, each increase doubles it. 1/4th is the minimum, so basically you can fly at 20 knots over London in slow motion.
(Traffic and water/other animations still move at regular speed)
It works very well, London is looking glorious today
The amount of detail is amazing, it just needs time to get it all in
