Horizontal is an orientation relating to, or in parallel with the horizon, and thus perpendicular to the vertical. A horizontal line goes from left to right (or vice versa) where a vertical line goes from top to bottom. Horizon The horizon is the line that separates earth from sky. ... An object is in a vertical position when it is aligned in an up-down direction, perpendicular to the horizon. ...

In Cartesian coordinates of the form (x,y) where it is frequently called abscissa, the horizontal axis is conventionally used for the x coordinate, with positive numbers extending to the right side of the vertical axis. The equation y=c, where c a constant, represents a horizontal line. In an complex number, the horizontal axis is used for the real component. Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ... A negative number is a number that is less than zero, such as −3. ... In mathematics, the complex numbers are an extension of the real numbers by the inclusion of the imaginary unit i, satisfying . ...

In perspective drawing, a set of parallel horizontal lines extending from the same vicinity must ultimately meet at a single point on the horizon known as the vanishing point. This is a common feature of pictures of straight roads or railway lines. The term Parallel has a number of important meanings: Parallel (geometry) occurs in geometry. ... A vanishing point is a point in a perspective drawing where parallel lines seem to converge into. ...

In construction, a spirit level helps orient structural members absolutely horizontal. A spirit level is an instrument designed to indicate whether a surface is level. ...

See also

• horizontal coordinate system