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No they are not. They're basically a collection of aerial photographs taken from other sources. That's why you can see seams between the pictures in some locatation or changes in quality (NH has lower resolution than MA if I remember right). The Massachusetts photos are taken from the Mass GIS (Geographic Information System) for example. The photographs are taken at a scale and assigned coordinates within the global coordinate system for used with mapping software. Google Earth provides a very user friendly format for the information. I only know this because I uses the Mass GIS alot for work - a lot of usefull information on their if you take the time to look for it and can figure out how to use it.
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