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In astronomy, geography, and related sciences and contexts, a direction or plane passing by a given point is said to be vertical if it contains the local gravity direction at that point. [1] Conversely, a direction or plane is said to be horizontal if it is perpendicular to the vertical direction. In general, something that is vertical can be drawn from up to down (or down to up), such as the y-axis in the Cartesian coordinate system.

Contents

1Historical definition

2Geophysical definition

2.1The plumb line and spirit level

2.2The flat earth approximation

2.3The spherical Earth

2.4Further complications

2.5Walls and floors

2.6Independence of horizontal and vertical motions

3Mathematical definition

3.1In two dimensions

3.2In three dimensions

3.3In the classroom

4Discussion

4.1Practical use in daily life

5See also

6References and notes

7Further reading

8External links

Historical definition

Girard Desargues defined the vertical to be perpendicular to the horizon in his 1636 book Perspective.

The word horizontal is derived from horizon,[2] whereas vertical originates in the late Latin verticalis, which is from the same root as vertex, meaning "highest point".[3]

Geophysical definition

Further information: Gravity of Earth and Figure of Ea

Explanation:

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