How to read a coordinate plane
A coordinate plane uses two number lines at right angles. The horizontal line is the x-axis, the vertical line is the y-axis, and their meeting point is the origin, written as (0, 0). Together the axes divide a full plane into four quadrants. Values to the right of the origin are positive x values, values to the left are negative x values, values above are positive y values, and values below are negative y values.
An ordered pair is written as (x, y). Read x first and move horizontally from the origin, then read y and move vertically. For (3, -2), move three units right and two units down. Repeating the phrase across first, then up or down helps beginners resist the common habit of reversing the two numbers.
- Quadrant I: x and y are both positive.
- Quadrant II: x is negative and y is positive.
- Quadrant III: x and y are both negative.
- Quadrant IV: x is positive and y is negative.
A point on an axis is not inside a quadrant. For example, (0, 4) lies on the y-axis and (-3, 0) lies on the x-axis. Calling that out early prevents a surprisingly persistent misconception.