Total flight restrictions are normally reserved over strategic targets or dangerous flight areas (ex. bombing ranges etc.)
Most major cities have primary airports and are considered class B airspace and have controlled airspace restrictions as such....
There are many areas where commercial and civilian aircraft are not allowed below a certain altitude because of dangerous flight areas, or military training areas, usually in close proximity of military bases.Most major cities have primary airports and are considered class B airspace and have controlled airspace restrictions as such....
Washington, DC is one such area where small planes are not allowed over. There are many large airports that don't even allow small aircraft under a certain weight limit to land on their runways in most cases. Denver International is one such airport, Wold-Chamberlin in Minneapolis/St. Paul is another, and Sky Harbor in Phoenix is another.