Height is the measurement of vertical distance, but has two meanings in common use. It can either indicate how "tall" something is, or how "high up" it is. For example one could say "That is a tall building", or "That airplane is high up in the sky". These can both be referred to as the height of the object, as in "The height of the building is 50m" or "The height of the airplane is 10 000m". When used to describe how high something like an airplane or mountain peak is from sea level, height is more often called altitude. Height is measured along the vertical (y) axis between a specified point and another point.

In mathematics

Dimensional models assert height as the third dimension, more accurately referred to as depth, the other two being length and width, which form a two-dimensional plane of reference. In this model, the dimension of height is measured along a line traveling from the point in question and intersecting the plane of reference at a 90 degree angle.

In geology

Although height is relative to a plane of reference, most measurements of height in the physical world are based upon a zero surface, known as sea-level. Both altitude and elevation, two synonyms for height, are usually defined as the position of a point above the sea-level. One can extend the sea-level surface under the continents: naively, one can imagine a lot of narrow canals through the continents. In practice, the sea-level under a continent has to be computed from gravity measurements, and slightly different computational methods exist, see Geodesy, heights.

In geodesy

Instead of using the sea-level, geodesists often prefer to define height from the surface of a reference ellipsoid, see Geodetic system, vertical datum.

Defining the height of geographic landmarks becomes a question of reference. For example, the highest mountain by elevation in reference to sea-level belongs to Mount Everest, located on the border of Nepal and Tibet; however the highest mountain by measurement of apex to base belongs to Mauna Kea in Hawaii, United States.

In aviation

In aviation terminology, the terms height, altitude, and elevation are not synonyms. Usually, the altitude of an aircraft is measured from sea-level, while its height is measured from ground level. Elevation is also measured from sea-level, but is most often regarded as a property of the ground. Thus, elevation plus height can equal altitude. But the term altitude has several meanings in aviation, see Altitude in aviation.

In human culture

Human height is one of the areas of study within anthropometry. As pointed out in an article 1 in The New Yorker, the average height of human populations appears to be a convenient metric for all the factors that make up a group's well-being. While height variations within a population are largely genetic, height variations between populations are mostly environmental.