CN Tower
"Guinness World Records" has called the CN Tower "the world's tallest self-supporting tower" and "the world's tallest free-standing tower". Although Guinness did list this description of the CN Tower under the heading "tallest building" at least once, it has also listed it under "tallest tower", omitting it from its list of "tallest buildings." In 1996, Guinness changed the tower's classification to "World's Tallest Building and Freestanding Structure". Emporis and the Council on Tall Buildings and Urban Habitat both listed the CN Tower as the world's tallest free-standing structure on land, and specifically state that the CN Tower is not a true building, thereby awarding the title of world's tallest building to Taipei 101, which is shorter than the CN Tower. The issue of what was tallest became moot when Burj Khalifa, then under construction, exceeded the height of the CN Tower in 2007 (see below).
List of tallest buildings by U.S. state and territory
The building heights compared here are calculated from the ground level to the architectural top and include heights of all habitable structures irrespective of number of occupied floors. Non-freestanding structures, observational towers, and communication towers are excluded (North Dakota boasts the largest guyed mast structure in the world), as are antennas extending from the structure top. However integral spires are included, facilitating One World Trade Center to be considered taller than Willis Tower, even though the highest occupied floor of Willis Tower is higher than that of One World Trade Center. The Council on Tall Buildings and Urban Habitat is considered the arbiter for any dispute. For more information, see building heights.