A scatter-plot graph is divided into four quadrants due to the (0, 0) intersection point of the horizontal axis (x-axis) and vertical axis (y-axis). This intersection point is called the origin. Both axes extend from negative infinity to positive infinity, resulting in four possible combinations of (x, y) points in the four respective quadrants. You should use Roman numerals to label your quadrants.
The upper-right quadrant, also referred to as the Quadrant I, will only contain points that lie within the range of 0 to positive infinity for both the x and y axis. Therefore, any point, indicated as (x, y), in the first quadrant will be positive at both x and y. So the product of the coordinates [ (+) x, (+) y] will be positive.
The upper-left quadrant, or Quadrant II, identifies only points to the left of zero (negative) on the x-axis and points above zero (positive) on the y-axis. Thus, any point in the second quadrant will be negative at the x value and positive at the y value. The product of these coordinates, [ (-) x, (+) y ], is negative.
The lower-left part of the grid, Quadrant III, identifies points less than zero on both the x and y axes. Any point within this quadrant will be negative at both x and y values. The product of these coordinates, [ (-) x, (-) y ], is always positive.
Quadrant IV, in the lower right of the graph, contains only points that are to the right of zero on the x-axis and below zero on the y-axis; therefore, all points in this quadrant will have a positive x value and a negative y value. The product of these coordinates, [ (+) x, (-) y ], will be negative.
About the Author
Matt Perdue is a medical student at an allopathic U.S. medical school. Beginning in 2010, he began writing science-related articles for eHow. He was also authored a paper for a medical journal exploring current recommendations for bone scans to diagnose osteoporosis.