The height of structures in the United States has been poorly documented. However, the data is a matter of public record, appearing in documents maintained by the Federal Aviation Administration (FAA) and Federal Communications Commission (FCC). This list is populated heavily by antenna masts. The engineering aspects of super-tall masts are highly specialized. Only four companies erect the majority of such structures: Doty Moore Tower Services (Cedar Hill, Texas); Kline Towers (Columbia, South Carolina); LeBlanc Royal Telecom (Oakville, Ontario); and Stainless Inc. (North Wales, Pennsylvania). The design and construction are largely governed by RS222E Electronic Industries Alliance standards. A mast costs between $0.7 and $1.1 million to build, while a mast costs $2.4 to $4 million. Prices generally vary depending on tower capacity and wind loading specifications. A common misperception is that landmarks such as the Stratosphere Tower are the tallest United States structures, but they are in fact the tallest buildings. Likewise Taipei 101 was often misrepresented as the world's tallest structure (although it was the tallest occupied building, before the certification of Dubai's Burj Khalifa as such), but in fact is far eclipsed by antenna towers in over a dozen states in the United States and in other countries. In the United States, the FAA and the FCC must approve all towers exceeding in height. Furthermore, it is very difficult to get permission for structures over high. The FCC presumes them to be inconsistent with the public interest, while the FAA presumes them to be a hazard to air navigation, resulting in poor airspace usage. A significant burden of proof is placed on the applicant to show that such a structure is in the public's best interests. Only when both agencies have resolved all legal, safety, and management concerns is such an application approved. Since 1978 the United States has maintained eleven tethered aerostats sites along the southern borders. These balloons rise to , carrying radar units for drug interdiction purposes. However, since the balloons are aided by buoyancy and are not permanent they are not considered true structures. State-by-state listing Alabama WTTO Television Tower (Birmingham WB-21) Windham Springs () Year Built: 1986 At 2,000 ft (610 m), this structure ties 19 others around the United States as the seventh-tallest structure in the world. RSA Battle House Tower Height: 745 ft (227 m) Mobile, Alabama Tallest Freestanding building in Alabama, and the tallest building on the coast between