The world's tallest human-made structure is the Burj Khalifa in Dubai, United Arab Emirates. The building gained the official title of "tallest building in the world" and the tallest self-supported structure at its opening on January 9, 2010. Burj Khalifa was developed by Emaar properties, designed by Skidmore, Owings and Merrill and built by BESIX, Samsung Construction and Arabtec. The second-tallest self-supporting structure and the tallest tower in the world is the Tokyo Skytree. The tallest guyed structure is the KVLY-TV mast. The Council on Tall Buildings and Urban Habitat, an organization that certifies buildings as the "World's Tallest", recognizes a building only if at least 49% of its height is made up of floor plates containing habitable floor area. Structures that do not meet this criterion, such as the CN Tower, are defined as "towers". There are dozens of radio and television broadcasting towers which measure over 600 metres (about 2,000 ft) in height, and only the tallest are recorded in publicly available information sources. Debate over definition The assessment of the height of artificial structures has been controversial. Because varying standards have been used by different organizations, the accepted height of these structures or buildings depends on which standards are accepted. The Council on Tall Buildings and Urban Habitat has changed its definitions over time. Some of the controversy regarding the definitions and assessment of tall structures and buildings has included the following: the definition of a structure, a building and a tower whether a structure, building or tower under construction should be included in any assessment whether a structure, building or tower has to be officially opened before it is assessed whether structures built in and rising above water should have their below-water height included in any assessment. whether a structure, building or tower that is guyed is assessed in the same category as self-supporting structures. Within an accepted definition of a building further controversy has included the following factors: whether only habitable height of the building is considered whether communication towers with observation galleries should be considered "habitable" in this sense whether rooftop antennas, viewing platforms or any other architecture that does not form a habitable floor should be included in the assessment whether a floor built at a high level of a telecommunications or viewing tower should change the tower's definition to that of a "building" Tallest structures This category does not require the structure