i dont believe in chem trails but why so many planes fly over the cities

[raaaid]

common sense would forbid planes flying over the cities but they do in consistent basis

so is it somehow enforced for the planes to fly over the cities?

for the record i dont believe at all the chem trail nonsense but this kinds of back it up

imho if they wanted to spread population control poisons they would do it with car fuel as they did with lead but this got me curious, any reason for planes flying over cities?