Quick question for you guys. Yesterday I was outside on the ramp of lovely JFK and was watching the departures, and in the distance saw LaGuardia's departures also. It got me wondering,exactly how do they coordernate the departures/arrivals at airports like NYC/Newark,MDW/ORD,and DFW/DAL? I know all about SIDs and STARS,but I figure at some point a airplane going into one airport would cross the departure/arrival path of another. So how does ATC do it?