A mountain is a land mass that rises above its surroundings, usually to a peak, and which is higher and generally steeper than a hill. The height of a mountain usually is measured from sea level to its summit. Using this method, Mount Everest, located on the border of Tibet and Nepal and measured at 29,028 feet (8,848 m), is considered to be the world's highest mountain. A measurement taken in 1999 of 29,035 feet (8,850 m) is considered by some to be more accurate, but it is not officially recognized.
There are two other accepted methods for determining the height of a mountain. One involves measuring the mountain from its base. When this method is employed, the results are generally said to indicate how tall a mountain is instead of how high it is. For example, Mount Mauna Kea, also known as "White Mountain," is a volcano of Hawaii whose base is on the floor of the Pacific Ocean. Mauna Kea, measured from its base to its peak, is 33,464 feet (10,200 m), making it the world's tallest mountain, even though it rises only about 13,800 feet (4,200 m) above seal level.
The tallest mountain might not be the highest, and the highest mountain might not be the tallest. Generally, mountain climbers seek to climb the higher mountains before the taller ones. This is because the highest mountain is measured from sea level, so it reaches higher into the heavens than the tallest mountain. This tends to give the highest mountains a more majestic appearance than the tallest ones.
A third method for determining the highest mountain involves measuring its elevation from the center of Earth. Using this method, Mount Chimborazo in the Central American country of Ecuador, is the world's highest mountain at 3,966 miles (6,384 kilometers) from Earth's center. Mount Chimborazo is located very close to Earth's equator, where the planet is widest, given that it is an oblate spheroid rather than a perfect sphere. Although Mount Everest rises higher above the sea than does Mount Chimborazo, Mount Everest's summit is closer to the center of Earth by approximately 1.35 miles (2.2 kilometers).
To give an accurate answer to the question of what the world's highest mountain is, one would need to know which method of measurement is to be employed. If the mountain is measured from sea level, Mount Everest is Earth's highest mountain. When measuring from the base to the summit, Mount Mauna Kea is the world's tallest mountain. Finally, if the question specifically asks for the highest mountain above the center of the Earth, Mount Chimborazo is the correct answer.