What does a blue segmented circle represent on a sectional chart?

A blue segmented circle on a sectional chart represents Class D airspace. This type of airspace is typically associated with airports that have an operating control tower and is used to provide air traffic control services to the aircraft operating in that vicinity. The segmented line indicates the horizontal boundaries of the airspace, and the blue color signifies that it is controlled airspace, meaning that communication with air traffic control is required prior to entering or operating within it.

Class D airspace usually extends from the surface up to a specified altitude, often around 2,500 feet, but this can vary depending on local regulations and the size of the airport. Pilots must be aware of the boundaries and requirements for Class D airspace to ensure safe operations around controlled airports. Understanding these chart symbols is essential for navigational skills and operational safety in aviation.