I may be wrong here but I thought that up to 400' the property owner owns the airspace. I believe that in the real estate one is able to purchase airspace. I think they call it sightlines. The intent is that if someone builds some high end apartments with a veiw of some landscape/ocean then he will want to protect his investment by buying up the airspace between his building and the view subject. This way someone can't come in and build a highrise that blocks the view thus bringing down his property value.