Define: horizontal and vertical

The horizon is the "apparent junction of earth and sky."

The following is a number line written horizontally.

```   <--+---+---+---+---+---+---+---+---+---+---+-->
-5  -4  -3  -2  -1   0  +1  +2  +3  +4  +5
```

The vertical is "perpendicular to the plane of the horizon or to a primary axis." [Perpendicular is "being at right angles to a given line or plane."]

The following is a number line written vertically.

```      ^
|
+5 +
|
+4 +
|
+3 +
|
+2 +
|
+1 +
|
0 +
|
-1 +
|
-2 +
|
-3 +
|
-4 +
|
-5 +
|
v
```
Right Angle

Perpendicular lines intersect and their point of intersection is called the origin. Perpendicular lines form four right angles at the origin. A right angle measures ninety degrees (`90°`).

With respect the Cartesian coordinate system, the horizonal line is the `x-axis` and the vertical line is the `y-axis`.

```           | <-- vertical-axis (y-axis)
|
|
|
--------o-------- <-- horizonal-axis (x-axis)
|\
| \
|  o is the origin
|
```

Note: The Cartesian coordinate system was developed by French mathematician and philosopher Rene Descartes in approximately 1637.

RoadHacker:: Horizon/Vertical Slideshow [opens new window]

Creator: Gerald Thurman [gthurman@gmail.com]
Created: 09 February 2005