The Cartesian plane is divided into four quadrants. These are numbered from I through IV , starting with the upper right and going around counterclockwise. (For some reason everybody uses roman numerals for this).

In Quadrant I , both the x – and y -coordinates are positive; in Quadrant II , the x -coordinate is negative, but the y -coordinate is positive; in Quadrant III both are negative; and in Quadrant IV , x is positive but y is negative.

Points which lie on an axis (i.e., which have at least one coordinate equal to 0 ) are said not to be in any quadrant. Coordinates of the form ( x,0 ) lie on the horizontal x -axis, and coordinates of the form ( 0,y ) lie on the vertical y -axis.