A straight line drawn on a grid can be described by a rule connecting the x and y coordinates of every point on the line. This is known as the Equation of the line.

A straight line can be drawn by joining two points plotted on a grid. The coordinates of the mid-point of the line and the length of the line can be calculated using the coordinate values.

Horizontal lines run left to right, parallel to the horizon, with slope 0 and equation y = k. Vertical lines run top to bottom, perpendicular to the horizon, with undefined slope and equation x = k.