The theme of these images is aviation. Airports are where the majority of planes take off from, as there are waterdromes/aerodromes that also handle aircraft traffic. Air traffic control is there to ensure the safe passage of planes throughout the skies, espiecially heavily congested airspace. The Cessna is one of the most populat general aviation planes in the world, used primarily for flight training and by private pilots. Clear skies is the conditions preferred when pilots go out to fly, as clear skies is generally associated with good weather, which causes no problems in flight and allows for a smooth ride.