Really interesting point. I would imagine that the other arcs may indicate a route. If the plane was on a certain arc at one time, then another arc the next time, another the next, etc., you might be able to look at where straight lines intersect the circles on successive tangents and figure out the plane's route (presuming, of course, that the plane was flying in a straight line). Which may be more information than they're comfortable with releasing, for any number of reasons...
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