Like a zipper, um, that large blue circle that's the sfr, a the special flight rules area. around washington, d c. it was instituted in the months and years after 9 11 any aircraft that's going to enter that blue zipper has to be in touch with with authorities on the ground , and you have to have a discreet code that you're squawking. now there's sort of an inner circle also outlined in blue around reagan airport. reagan airport is the solid blue dot in the center of this map. obviously that's very close to the capital, the pentagon, other sites that were attacked or potentially attacked on 9 ...