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 tenants in One World Trade Center
The original One World Trade Center (also known as the North Tower, Tower 1, Building One, or 1 WTC) was one of the Twin Towers of the original World Trade Center in New York City. It was completed in 1972, standing at a height of , and was the tallest building in the world until being surpassed by the Sears Tower in Chicago in 1973. It was distinguishable from its twin, the original Two World Trade Center, also known as the South Tower, by the telecommunications antenna on its roof. Including the antenna, the building stood at a total height of . The building's address was One World Trade Center, with the WTC complex having its own ZIP code of 10048 due to its large size.